This paper designed a harmonic analysis module which is based on a new method of extracting zinc oxide arrester impedance current． With Digital Signal Processor( DSP) as the core，using ADS8556 which is highspeed to transform analog signal，and using TMS320LF2812 to process data，the module will get characteristics: fundamental current amplitude，harmonic amplitude of whole leakage current which required by new method forextracting impedance current． This paper introduced the system hardware circuit and designed the software program on this basis like the A /D sampling subprogram，filter algorithm subprogram，integral algorithm subprogram，FFT( Fast Fourier transform) algorithm subprogram，resistance current extraction subprogram，etc． Data will be collected and then processed by using this system and the final the resistance leakage current which is the key tomonitoring will be obtained． This paper also verified the results by software simulation and the actual analog circuit testing． The result confirmed that the module can well meet the needs of the system to do harmonic analysis．