A dynamic simulation system for voltage source converter based high voltage direct current（VSC-HVDC）based on the modular multilevel converter（MMC）topology is described，which is a back to back simulation system.With a real project as the prototype supplier，equivalent simulation for the AC system，converter valves，converter transformers，and DC cables are briefly treated，while the parameter design and simulation ratio design for AC system，DC system，converter valves， converter transformers are given.The measurement units for this system are the same as those for the project.Fault simulation and fault point setting are also dealt with.Finally，the results for steady-state and fault ride-through test are presented.The waves from the simulation system are compared with those of the field project，the results showing the dynamic simulation system can accurately simulate the steady-state and transient characteristics of the actual project as provide experimental verification for the design of control and protection system of VSC-HVDC.