Abstract: Through the subsystems division of multi terminal HVDC(MTDC) system based on voltage source converter(VSC), a kind of equivalent model for accessing the reliability evaluation of the VSC MTDC transmission system is presented based on state space method, which can avoid the dimension disaster due to lots of components, then reduce the amount of calculation. In addition, the reliability index can also be calculated besides the steady state probability, such as the failure frequency index, duration time index. The reliability calculation results of 5 terminal VSC MTDC transmission system verify the correctness and effectiveness of this method. The weak link can be found through parameter sensitivity analysis of system equipments, and results show that the submarine cables between offshore and onshore and the offshore converters are the important elements that influence system reliability.