在分析用IIR陷波滤波器来抑制局部放电在线监测中周期性干扰的基础上 ,提出和论述了级联式IIR陷波滤波器基本原理及简明设计方法。模拟仿真和现场实验证明这种滤波器能有效的抑制局部放电在线监测系统中的周期性干扰。对于采样频率低的窄带系统 ,采用该滤波方法能在滤波同时 ,得到一个周波里的放电波形。 Based on the analysis of the IIR notch filter to suppress the periodic disturbance in PD online monitoring, the basic principle and concise design method of cascaded IIR notch filter are proposed and discussed. Simulation and field experiments show that this filter can effectively suppress the periodic disturbance in PD monitoring system. For the narrow sampling frequency of the narrowband system, using the filter method can filter at the same time, get a cycle of the discharge waveform.