diff --git a/DASMatrix/processing/backends/numba_backend.py b/DASMatrix/processing/backends/numba_backend.py
index ecdf50d..c97b3aa 100644
--- a/DASMatrix/processing/backends/numba_backend.py
+++ b/DASMatrix/processing/backends/numba_backend.py
@@ -4,10 +4,36 @@
 
 import numba
 import numpy as np
+from scipy import signal
 
 from ...core.computation_graph import FusionNode
 
 
+@numba.njit(fastmath=True)
+def sos_filter_sample(val, sos, zi):
+    # sos: (n_sections, 6)
+    # zi: (n_sections, 2)
+    # Direct Form II Transposed
+    for s in range(sos.shape[0]):
+        b0, b1, b2, a0, a1, a2 = sos[s]
+
+        # In Scipy, a0 is usually 1.0. If not, we should normalize.
+        # But usually sos output from scipy is normalized.
+
+        x = val
+        # y[n] = b0*x[n] + z1[n-1]
+        y = b0 * x + zi[s, 0]
+
+        # z1[n] = b1*x[n] - a1*y[n] + z2[n-1]
+        zi[s, 0] = b1 * x - a1 * y + zi[s, 1]
+
+        # z2[n] = b2*x[n] - a2*y[n]
+        zi[s, 1] = b2 * x - a2 * y
+
+        val = y
+    return val
+
+
 class NumbaBackend:
     """Numba 高性能计算后端。"""
 
@@ -53,7 +79,7 @@ def execute(self, node: FusionNode, data: np.ndarray) -> np.ndarray:
     def _prepare_aux_params(
         self, node: FusionNode, data: np.ndarray
     ) -> List[np.ndarray]:
-        """为需要归约的算子准备参数 (如 mean, trend)。"""
+        """为需要归约的算子准备参数 (如 mean, trend, filter coeffs)。"""
         params = []
         n_samples, n_channels = data.shape
 
@@ -93,6 +119,22 @@ def _prepare_aux_params(
                 means = np.mean(data, axis=0)
                 params.append(means.astype(data.dtype))
 
+            elif op.operation == "bandpass":
+                # Calculate SOS coefficients
+                low = op.kwargs.get("low")
+                high = op.kwargs.get("high")
+                order = op.kwargs.get("order", 4)
+                fs = op.kwargs.get("fs", 1000.0) # Default to 1000 if not provided
+
+                nyq = 0.5 * fs
+                sos = signal.butter(
+                    order, [low / nyq, high / nyq], btype="band", output="sos"
+                )
+                # SOS shape: (n_sections, 6)
+                # It is global for all channels,
+                # but Numba kernel needs it as an argument
+                params.append(sos.astype(data.dtype))
+
         return params
 
     def _get_kernel_signature(self, node: FusionNode) -> str:
@@ -108,6 +150,8 @@ def _compile_kernel(self, node: FusionNode, has_aux: bool):
         # 辅助参数名列表 (在 kernel 签名中使用)
         aux_arg_names = []
 
+        pre_loop_code = [] # Code to execute before inner loop (inside j loop)
+
         for op in node.fused_nodes:
             if op.operation == "detrend":
                 # 需要 slope 和 intercept
@@ -133,24 +177,36 @@ def _compile_kernel(self, node: FusionNode, has_aux: bool):
                 ops_code.append(f"val = val * {factor}")
 
             elif op.operation == "bandpass":
-                # Placeholder: Pass-through
-                # TODO: Implement IIR/FIR filter state or sosfilt
-                pass
+                sos_name = f"aux_{aux_idx}"
+                aux_arg_names.extend([sos_name])
+                aux_idx += 1
+
+                # Setup state variable for this channel
+                zi_name = f"zi_{aux_idx}"
+                # Get n_sections from sos shape at runtime or assuming fixed?
+                # We can use sos_name.shape[0]
+                pre_loop_code.append(
+                    f"{zi_name} = np.zeros(({sos_name}.shape[0], 2), dtype=inp.dtype)"
+                )
 
-            # TODO: Add filter support (requires stateful loop or simple FIR/IIR)
+                # Apply filter
+                ops_code.append(f"val = sos_filter_sample(val, {sos_name}, {zi_name})")
 
         kernel_body = "\n            ".join(ops_code)
+        pre_loop_body = "\n            ".join(pre_loop_code)
 
         # 构建函数签名
         base_args = ["inp", "out"]
         all_args = base_args + aux_arg_names
         args_str = ", ".join(all_args)
 
+        # Swapped loops: Parallel over cols (channels), Serial over rows (time)
         code = f"""
 def fused_kernel({args_str}):
     rows, cols = inp.shape
-    for i in prange(rows):
-        for j in range(cols):
+    for j in prange(cols):
+        {pre_loop_body}
+        for i in range(rows):
             val = inp[i, j]
             {kernel_body}
             out[i, j] = val
@@ -160,6 +216,8 @@ def fused_kernel({args_str}):
             "numba": numba,
             "prange": numba.prange,
             "abs": abs,
+            "np": np,
+            "sos_filter_sample": sos_filter_sample
         }
 
         exec(code, global_scope)
diff --git a/DASMatrix/processing/planner/optimizer.py b/DASMatrix/processing/planner/optimizer.py
index 1aa5871..36da49f 100644
--- a/DASMatrix/processing/planner/optimizer.py
+++ b/DASMatrix/processing/planner/optimizer.py
@@ -20,7 +20,6 @@
     "envelope",
     "normalize",
     # 滤波器操作 (需要 SciPy)
-    "bandpass",
     "lowpass",
     "highpass",
     "notch",
@@ -33,6 +32,7 @@
     "demean",
     "abs",
     "scale",
+    "bandpass",
 }
 
 
diff --git a/tests/unit/test_numba_bandpass.py b/tests/unit/test_numba_bandpass.py
new file mode 100644
index 0000000..62d52fd
--- /dev/null
+++ b/tests/unit/test_numba_bandpass.py
@@ -0,0 +1,114 @@
+"""Test Numba implementation of bandpass filter."""
+
+import numpy as np
+from scipy import signal
+
+from DASMatrix.core.computation_graph import (
+    FusionNode,
+    OperationNode,
+    SourceNode,
+)
+from DASMatrix.processing.backends.numba_backend import NumbaBackend
+
+
+class TestNumbaBandpass:
+    """Test Bandpass implementation in Numba Backend."""
+
+    def test_bandpass_correctness(self):
+        """Verify that Numba bandpass matches Scipy implementation (causal sosfilt)."""
+        # Setup data
+        rows = 2000  # Time
+        cols = 5     # Channels
+        fs = 1000.0
+        # Create random signal
+        np.random.seed(42)
+        data = np.random.randn(rows, cols).astype(np.float64)
+
+        # Create Graph Node
+        source = SourceNode(data, name="source")
+        # bandpass: low=10, high=100
+        low = 10.0
+        high = 100.0
+        order = 4
+
+        op_bandpass = OperationNode(
+            operation="bandpass",
+            inputs=[source],
+            name="bandpass_op",
+            kwargs={"low": low, "high": high, "order": order, "fs": fs}
+        )
+
+        # Fusion Node
+        fusion_node = FusionNode([op_bandpass], name="fused_bandpass")
+
+        # Execute with NumbaBackend
+        backend = NumbaBackend()
+        result_numba = backend.execute(fusion_node, data)
+
+        # Execute with Scipy (Reference)
+        nyq = 0.5 * fs
+        sos = signal.butter(
+            order, [low / nyq, high / nyq], btype="band", output="sos"
+        )
+        # We implemented sosfilt (Direct Form II Transposed), causal.
+        # Scipy default sosfilt is axis=-1, but here data is (Time, Channel).
+        # We need axis=0.
+        result_scipy = signal.sosfilt(sos, data, axis=0)
+
+        # Comparison
+        # Since we use float64, precision should be high.
+        # sosfilt might have slight numerical differences
+        # due to implementation details or order,
+        # but Numba implementation follows standard DF-II Transposed logic.
+
+        np.testing.assert_allclose(
+            result_numba,
+            result_scipy,
+            rtol=1e-5,
+            atol=1e-5,
+            err_msg="Numba bandpass result does not match Scipy sosfilt"
+        )
+
+    def test_bandpass_chain(self):
+        """Verify bandpass works in a chain (e.g. detrend -> bandpass -> abs)."""
+        rows = 1000
+        cols = 3
+        fs = 500.0
+        data = np.random.randn(rows, cols) * 10.0 + 100.0 # Offset
+
+        # Add trend
+        t = np.arange(rows)
+        trend = t.reshape(-1, 1) * 0.1
+        data += trend
+
+        # 1. Detrend
+        # 2. Bandpass
+        # 3. Abs
+
+        # Reference Scipy Calculation
+        # Detrend
+        step1 = signal.detrend(data, axis=0)
+
+        # Bandpass
+        sos = signal.butter(4, [5.0/250.0, 50.0/250.0], btype="band", output="sos")
+        step2 = signal.sosfilt(sos, step1, axis=0)
+
+        # Abs
+        expected = np.abs(step2)
+
+        # Numba Calculation
+        source = SourceNode(data)
+        op1 = OperationNode("detrend", [source])
+        op2 = OperationNode(
+            "bandpass",
+            [op1],
+            kwargs={"low": 5.0, "high": 50.0, "order": 4, "fs": fs},
+        )
+        op3 = OperationNode("abs", [op2])
+
+        fusion_node = FusionNode([op1, op2, op3])
+
+        backend = NumbaBackend()
+        result_numba = backend.execute(fusion_node, data)
+
+        np.testing.assert_allclose(result_numba, expected, rtol=1e-5, atol=1e-5)