An Monitor& Diagnosis Support System for Nuclear Power Plants (NPPMDS) is developed in the embedded real-time operation system VxWorks in this paper. NPPMCS includes data collection and validation unit, operation monitoring unit, fault diagnosis unit, alarm analysis unit, operation procedures and Human-machine interface and so on. The paper introduces the design and implementation of NPPMDS including the structure of the NPPMDS and the main function units. In order to confirm the validity of this system, the SGTR simulation experiment was carried out on a full scale simulator of nuclear power plants. The experimental results show that the system provides operation support, the load and pressure for the workers can be reduced and the safety of nuclear power plants can be enhanced.