By combining the merits of real-time digital simulation and dynamic physical simulation，power hardware-in-the-loop（PHIL）has become the crucial means of research on the physical properties and integration techniques of renewable energy and energy storage devices in the future.As the interface algorithm is the key to the PHIL system，the stability and accuracy characteristics of the interface algorithms are studied and established.The damping impedance method（DIM）interface is simplified，the stability of the simplified DIM interface and ideal transformer model（ITM）interface is studied.The impact of simplified DIM interface on the digital simulation system is analyzed，and it is discovered that，when the damping impedance in the virtual electrical system（VES）matches the equivalent impedance in the hardware under test（HUT），the simplified DIM interface is characterized by transparency which means that the response in the digital simulation is not affected by the delay due to the interface.The characteristics of simplified DIM interface and ITM interface with respect to the response accuracy of the HUT are studied for the HUT with and without a power source.It is concluded that the driving capability of the ITM interface is better than that of the DIM interface when the HUT has a power source.Based on the results of analysis，the principles of selecting a suitable interface algorithm under different conditions are given.