With the rapid development of rail transit, the operation and maintenance environment of high-speed EMUs becomes more complex, leading to frequent new and old faults. Therefore, an efficient, intelligent and accurate maintenance method is very important. Aiming at the problems of complex faults, outdated maintenance methods and lagging maintenance manual in the maintenance work of EMU coupler, an auxiliary maintenance method of EMU coupler based on mixed reality technology was proposed. With the help of mixed reality and data interaction technology, the overall model and technical framework of MR Auxiliary maintenance for the fault of EMU coupler were constructed. The key technologies such as virtual-real registration fusion, intelligent fault diagnosis, data information interaction and maintenance assistance guidance were studied, and various human-computer interaction assistance maintenance methods such as gesture recognition and eye tracking based on Unity3D-HoloLens were realized. Finally, an example of MR Assisted inspection for faults of close-connected coupler air path and control system of EMU verifies the effectiveness of the proposed method.