Aiming at the problem of poor surface quality of multi-stage inner conical hole parts in electrochemical machining, a hydraulic self driving rotating magnetic field assisted electrochemical machining method is proposed, a hydraulic self driving rotating flow field model is established and simulated, and the structure of cathode tail blades is optimized. The simulation results show that when the number of cathode blades is 3 and the thickness of blades is 0.8mm, When the electrolyte flow rate is not less than 5m/s, the impeller at the tail of the cathode mandrel can rotate stably. A hydraulic self driving rotating magnetic field assisted electrochemical machining cathode is designed. When the machining voltage is 10V, the electrolyte temperature is 30 ℃, the electrolyte pressure is 1.6Mpa, the cathode feed speed is 5mm / min, and the electrolyte is 5%NaCl+16%NaNO3+4%NaClO3 composite electrolyte, the comparative experimental study of multi-stage inner conical hole electrochemical machining process with and without rotating magnetic field is carried out, The results show that the surface roughness of the workpiece without magnetic field is Ra0.847μm under the same processing parameters . With the addition of rotating magnetic field, the surface roughness of the workpiece is Ra0.437μm. The surface quality was improved by 48.41%.