Abstract: Recently,with the changes of structure of power grid,the method of injection signal has been used widely in the measurement of capacitance current.There are two bottleneck problems were not resolved in process of practical application of the method,namely the problems of signal source and 50 Hz trapped wave.Aiming at the two problems,the paper proposed a new method of using digital signal processor TMS320F2812 and DDS technology to realize measurement of capacitance current.It introduced design of hardware and software of signal source and design of 50 Hz wavetrap in details,and gave whole implementation of the method.The experiment proved that the method has characteristics of accuracy, conveniency and safety in measurement of capacitance current.