Abstract: The fault diagnosis system can serve as an important auxiliary tool of advanced instrument and control system of nuclear power plant. This paper introduces a kind of state monitoring and fault diagnosis system for nuclear power equipment. The system whose system program was coded with Visual Basic 6.0 was integrated with functions of data acquisition, state monitoring and fault diagnosis and was robust and easy to operate. In order to confirm the validity of this system, the simulation experiment was carried out on a nuclear power plant simulator. The experimental results show that the system can completely and accurately identify the typical faults of nuclear power equipment.