Analysis is carried on the risks of the DC system with common ground electrode in the process of monopolar metallic and ground return mode conversion，including the impact on equipment，such as converter transformers and switches，as well as control and protection system. A new wiring solution for solving the influence is proposed to install a current-limiting resistor and its bypass switch between the high-speed grounding switch （HSGS） and the grounding grid of the converter station. The resistance design method of the grounding current-limiting resistor is also given. The limited current and the neutral line voltage in the process of DC operation mode conversion are proposed based on theoretical analysis and verified by commissioning. The influence of the grounding method on the DC system during the fault transient conditions are analyzed by PSCAD/EMTDC simulation. The results show that the solution can effectively solve the mutual influence of the common grounding electrode on the converter station during the conversion process of the DC operation mode，and does not affect the steady-state and transient stress requirements of the polar line and neutral line equipment. For the DC control and protection design，only the sequence control needs to be modified for the built project，and the protection configuration does not need to be modified.