A magnetic field generator for compression plasma discharge channel of micro EDM deposition has been designed. The self-magnetic field type by discharge current in the plasma channel of micro EDM deposition process has been analyzed. It presents a stable gradient annular magnetic field with the variables of discharge current and the distance from the discharge center. The force analysis of the charged particles in the discharge plasma channel under the self-magnetic field has been researched. The design principles of external magnetic field for enhancing the self-magnetic field to influence the machining performance have been put forward. Then, the structure type and dimension of external magnetic field generator have been determined. Results show that the external magnetic generator has the capability to enhance the self-magnetic field for compression plasma discharge channel with the proper structure parameters. With the increasing of the number of turns to 20, the external magnetic generator can influence the range of 0.10mm to 0.20mm from discharge channel center.