The overvoltage and insulation coordination are the key technologies in the Ningdong-Shandong ±660 kV HVDC transmission project, and have great influence on the feasibility, reliability, economy of the project. In this paper, combined with the insulation coordination features of the project, the power frequency, harmonic vibration, operation and lightning overvoltage level are analyzed by the overvoltage electromagnetic transient simulation. Based on the simulated results, the insulation level of equipment in converter station is determined, providing references for the matching of the engineering equipments.