Since the surrounding of mediumfrequency power supply exist a large number of harmonics and the electromagnetic interference, it unable to work normally. Firstly,This paper introduces the application and problems of the medium frequency power supply. In order to improve the antiinterference ability of the microprocessor in the mediumfrequency power supply application system, the article designed antiinterference measures from four aspects of inhibition of interference sources, interference sources of segregation, interference reduction and the improvement of its antiinterference ability. Last,using MATLAB simulation software to establish the simulation model of the 12phase rectifier to verify whether the design of the filter has the rationality through simulation analysis was made on whether to place the RLC series filter in the side of power supply. The simulation results show that placing the RLC series filter in the side of power supplyt can effectively restrain harmonics.