In proportion to the rapid increase in the number of Web users, web attack techniques are also getting more sophisticated. Therefore, we need not only to detect Web attack based on the log analysis but also to extract web attack events from audit information such as Web firewall, Web IDS and system logs for detecting abnormal Web behaviors. In this paper, web attack detection system was designed and implemented based on integrated web audit data for detecting diverse web attack by generating integrated log information generated from W3C form of IIS log and web firewall/IDS log. The proposed system analyzes multiple web sessions and determines its correlation between the sessions and web attack efficiently. Therefore, proposed system has advantages on extracting the latest web attack events efficiently by designing and implementing the multiple web session and log correlation analysis actively.