To improve the DC voltage anti-interference ability of a vehicle-grid coupling system under multi-operating conditions, a sliding mode control strategy of EMUs grid side rectifier based on a sliding mode observer (SMO+SMC) is proposed. First, through building the mathematical model of CRH3 EMUs in a dq coordinate system, the design equation of the sliding mode observer is derived. Then, the sliding mode observer is used to observe the output power of the traction motor in real time, and the voltage control module of the outer loop of the sliding mode control is supplied to realize the combination of the sliding mode observer and the sliding mode control. Finally, PI, sliding mode control and SMO+SMC are applied to the simulation model of CRH3 EMUs. In addition, the DC voltage control effect of the rectifier side under multiple working conditions is analyzed and verified, and then a semi-physical experiment is carried out based on the HIL small step real-time simulation test platform. The simulation and experimental results show that the SMO+SMC strategy can improve the DC voltage anti-interference ability and the stability of grid side voltage and current when multiple vehicles are connected to the grid. This work is supported by the Key Project of High Speed Rail Joint Foundation of National Natural Science Foundation of China (No. U1434203).