With the popularity of the Internet, network security has been paid more and more attention. Application of network security has become important contents for lots of experts and scholars to study. This work began with the concept and features of computer network technology. Then it analyzed the threats of the computer network, including system vulnerabilities, viruses and Trojans, transport protocol, etc. Finally, it studied security measures including installing patch timely, installing anti-virus software and firewalls, developing new transport protocols, etc. It is hoped that it can provide a reference for the actual security work.