The provided method and system is a method and system for analyzing the malicious code protocol and generating harmful traffic. The harmful traffic generating method constructs packet protocol information for generating a first attack packet corresponding to the TCP/IP protocol for generating network traffic, and then sets network vulnerability scanning for generating a second attack packet for carrying out network vulnerability scanning. Subsequently, the method constructs attack information for generating a third attack packet in the form of denial of service, and generates harmful traffic using the packet protocol information, network vulnerability scanning and attack information. Accordingly, performance testing of the network security system against malicious code attacks such as the Internet worm can be performed.