In order to provide reference for the popularization and engineering application of flexible DC technology in our country, this paper mainly studies the simulation of internal overvoltage in converter station of offshore wind power flexible DC transmission system with different main wiring modes. Firstly, the connection mode, system model and parameters of symmetrical monopole and symmetrical bipolar are introduced. Then, based on the key fault conditions and observation points in the converter station, the simulation model of the offshore wind power flexible DC system with symmetrical monopole and symmetrical bipolar connections is built in the PSCAD/EMTDC, and the lightning arrester protection scheme is configured respectively. Finally, the internal overvoltage and the maximum energy of arrester generated by these two main wiring models on the key equipment of converter station under typical faults are simulated and analyzed, which provides an important basis for the research on the insulation coordination of converter station and the selection of related equipment in the flexible DC project of offshore wind power in the future.