Abstract: An engineering nuclear power plant simulator was developed aimed to provide a close-loop analysis tool during the design of new Instrumentation and Control（I＆C） systems. Firstly, a simulation platform with a distributed and parallel computing architecture was developed based on.NET environment. Different functional modules, mainly including the thermal-hydraulic module, the control system module and the human-machine interface module, were integrated in the platform to complete the complex model design. Then, based on the simulation platform, a pressurized water reactor simulator was built. Taking RRC Design Manual as a reference, the performance of the simulator, especially the performance of I＆C systems, was evaluated and modified. The final result of the simulator is qualitative accord with the RRC Design Manual and the steady value agrees well with the RRC Design Manual before and after transients.