Our society will enter a comprehensive network era, which is mainly featured with electronic commerce. Our life will be more closely with the computer network. We can say that our life cannot go without computer network. So there is no doubt that network security is very important for us. We can't imagine how to survive in unsafe computer network, and how does the information be transmitted truly, completely, effectively and legally. So here we will discuss the topic of network security. This paper includes the meaning and characteristics of network security, the threats and attacks faced by computer network, security measures safeguarding network; network security technology introduction, classification and relationship; overview of firewall, firewall key technology; examples of firewall application construction; future development tendency of firewall technology and products, etc.