The difficulty of designing a virtual scene based on Virtools is to design the semi-physical interface. To solve this problem, the Virtools SDK was used for constructing a communication building block(BB) by calling relevant application program interface(API) function to achieve communication between physical system and the virtual scene. Then the Virtools SDK callback function was used to control the switch of the semi-physical interface correctly. At last, the building block was integrated into the virtual scene and our expectation was achieved. The results indicate that development of semi-physical interface based on Virtools' SDK is feasible.