The invention discloses a safety net gate system special for nuclear power and a data processing method. The security gateway system comprises an intranet host, an extranet host and a data ferry module; the data ferry module is divided into an intranet side data ferry module and an extranet side data ferry module, which are in communication with an intranet host and an extranet host through PCIE interfaces respectively; the intranet-side data ferry module and the extranet-side data ferry module communicate with each other through two paths of unidirectional optical fibers. Other physical feedback path can be avoided, the intranet side data ferry module caches a data packet transmitted by the intranet host through the PCIE interface; and the cached data packet is analyzed and the data packet is transmitted to the external network side data ferry module through a unidirectional optical fiber, the data packet transmitted by an internal network side data ferry module through two paths of unidirectional optical fibers are cached by the external network side data ferry module, and consistency comparison and CRC verification are performed on the two paths of data packets. According to theinvention, the reliability of data transmission and the system security are improved.