An auto impulse current measuring system for surge protective device (SPD) with power source was studied, the system was composed of impulse current generator, programmable logical controller (PLC), couple and decouple network (CDN), power tracking circuit and intelligent digital peak measuring instrument. It can carry common and different mode tests for SPD, the maximum impulse current amplitude is up to 200 kA, the accuracy of measuring impulse peak is less than plusmn1%, and the accuracy of phase tracking power frequency is less than plusmn3deg