Abstract: Flexible operation mode is one of the VSC-HVDC system’s advantages, and the power system may continue to operate in the future with different grid structures under maintenance and other working conditions. However, for the VSC-HVDC system with overhead transmission lines, the DC lines are prone to single-pole grounding fault. Therefore, it is necessary to study the overvoltage of the DC lines with single-pole grounding fault for different grid structures. In this paper, a VSC-HVDC overvoltage model is built based on the ring-type four-terminal DC grid project, and the transient overvoltage characteristics of the VSC-HVDC system with the DC-side grounding fault are studied. The overvoltage levels of key nodes and equipment inside and outside the converter station are analyzed for four different VSC-HVDC grid structures with single-pole grounding fault occurring in the DC line. The results show that the system has a relatively low overvoltage level for the pseudo-U shaped structure, but has a relatively high overvoltage level for the broken-line shaped and real-U shaped structures. The system structures have the similar impact tendencies on the voltage to ground at the valve-side of converter transformer and on the overvoltage of the converter station bus.