The wide use of network improves security risks, but the traditional network security tools are single-functional and they are difficult to extend and manage. These security tools can’t fulfill the need of users. The paper presents a network security oriented language: NSL (Network Security Language). The language provides a common abstract layer of all kinds of security application. It can be used to construct multifunctional, distributed and extendable security applications, satisfying various and emergent security requirements. The paper describes its network oriented structures, features and three security mechanisms. The NSL interpreter implementation is also analyzed by the performance test. At last, the paper puts forward improving work which will be done in the future.