The joint research of automatic test and fault diagnosis has been widely used in the field of electronic equipment. For the problem of low test efficiency of the radio frequency index of communication equipment in development phase and difficult of the test fault location, this paper developed the automatic test system based on virtual instrument and intelligent fault diagnosis system which can be applied to the automatic test of radio frequency index. The knowledge base and reasoning mechanism of expert system are used in the fault diagnosis system. The interpretation mechanism adopts the method of prefabricated text. The actual results show that the system can effectively and accurately complete the automatic test of RF index, and the problems in the testing process has been accurately positioned.