The distributed partial discharge test during AC withstand voltage test of power cable is an effective means to detect the minor defects in the cable body and its accessories. In order to solve some key technical problems of this technology in the practical application, effects of grounding modes on the partial discharge signal accessed are studied through numerical simulation and calculation in this paper. The effect of grounding mode on induced overvoltage of metal protection layer in insulation fault is simulated. The simulation results show that cross connection joint should be changed into a straight type in the cable voltage synchronous distributed partial discharge test, and be grounded through the voltage limiter or grounded directly. The cable voltage synchronous distributed partial discharge test has been applied widely in Guangzhou Power Grid in recent years, and the cable defects have been found sucessfully and located accurately. The research results provide important references for the completion of power grid cable projects.