To improve the quality of network security service, the physical device service mode in traditional security service is improved, and the NFV network security service system is constructed by combining software defined networking (SDN) and network function virtualization technology (NFV). Where, network service is provided in the form of security service chain, and Web security scan service is taken as the task, finally the implementation and verification of the system are carried out. The test result shows that the security service system based on NFV can balance the load between the security network service devices in the Web security scan, which proves that the network security system based on software defined security and NFV technology can meet certain service requirements, and lays the research foundation for the improvement of the subsequent user network security service.