Abstract: In order to resolve the problem of hidden trouble about safety in existing capacitiance current measurement device,the paper put forward a design scheme of on-line measurement device of capacitance current based on DSP,introduced the measurement principle,design of hardware,and software of the device.The device uses the signal-injection method to measure capacitance current of power network which uses arc-suppression coil to on-line inject signal range from 20 Hz to 80 Hz with step 0.2 Hz and equal amplitude into secondary side of arc-suppression coil,uses DSP to process feedback signal to get resonate frequency of power network system,then indirectly gets capacitance current.The device solves the problem of safety of mesuring capacitiance current.