With the further development of new energy bases on desert and wasteland, the transmission technology based on modular multilevel converter (MMC) solves the problems such as commutation failure and inability to connect with weak AC systems. The number of semiconductor switches in a MMC for High Voltage Direct Current (HVDC) transmission creates a challenge for electromagnetic transient simulation programs, as it can significantly increase the simulation time. This paper presents a method based on average model for the converter part. The proposed model based on advanced digital power system simulator (ADPSS) was used to achieve precise simulation of MMC-HVDC transmission systems through the digital analog hybrid real-time simulation. Take a typical case during the site commission test programs at Yu to E ± 420kV back-to-back MMC-HVDC transmission project for example, we will give a detailed comparison between the simulation test of the presented model and the actual project. The results shows that the simulation system is consistent with actual project, which can be used to simulate the large-scale AC-DC interconnection power grid accurately.