Abstract: Fangjiashan nuclear power plant environmental radiation and meteorological monitoring system（KRS） signals from Fangjiashan off-site emergency center building. There are security risks of network attacks, affectting the stable operation of the whole unit DCS. To solve potential risk of information security, the project design KRS signal is seperated from the current DCS network, and NASPIC is used as the preferred solution to this modification project. This paper introduces the principle of NASPIC, the main function of the equipment, network configuration, software configuration and the application in Fangjiashan nuclear power plant. The modification project has been completed and the system operates normally.