This paper describes the development process of general interface adapter in the digital circuit fault diagnosis system based on VXI. After giving overall description of fault diagnosis system and VXI bus, the paper presents a method of solving the problem about load matching and interface matching, and realizes the function of identification to read and write on the memory of interface circuit and to control chip selection. The method of identity installation in interface circuit to be selected is to give an ID number and add a memory to interface circuit to ensure the accuracy and effectiveness. The paper also describes the method of self diagnosis in the interface circuit that is the key to whole fault diagnosis system.