Abstract: With the development of large-scale offshore wind power, multi-terminal DC（MTDC） system has gained more and more attention in the grid connection planning of offshore wind power due to its flexible network structure and control capability.Focusing on the planning requirements for offshore wind power clusters to be connected to the onshore power grid through the MTDC system, for the MTDC network topology optimization problems including the number of the point of common coupling（PCC） connected to the onshore power grid, the location and the capacity etc., a definition method of MTDC network topology matrix is proposed. This method can be intuitively used for the construction of small-signal models and the calculation of investment costs with different network topologies of the MTDC system, and a comprehensive optimization method is constructed that takes into account the investment economy of MTDC systems and the effect of MTDC system access on the stability of onshore AC power grids. The results of the example analysis show that the proposed model and method can effectively optimize the selection of the multi-network topology scheme of the MTDC system, which not only ensures the economy of the system, but also helps to improve the static stability of the planning scheme.