As interconnecting means connected the physical side and the digital simulation side in hardware in the loop, power interface play a decisive role for the stability and accuracy of hybrid simulation system; so the design of power interface and its control strategy is a key for hardware in the loop. The DC voltage fluctuation caused by load power mutation and amplitude error in the power amplification process is the two main factors of the power interface stability and accuracy. Based on hardware in the loop,this paper design its power interface and put forward the four-quadrant converter power interface device based on three single-phase H-bridge configuration. On this basis, considering the stability and accuracy of the power interface, study its control strategy employed. In order to ensure good dynamic performance and DC voltage stable of power interface, a DC voltage optimum control strategy based on current feed-forward control is proposed; considering the accuracy and stability of signal amplification,a composite control based on repetitive control for the inverter is proposed.Finally,the hardware in the loop tests verify the effectiveness of the proposed power interface and its control strategy.