Risk analysis process, which identifies vulnerabilities and threat causes of network assets and evaluates expected loss when some of network assets are damaged, is essential for diagnosing ISP network security levels and response planning. However, most existing risk analysis systems provide only methodological analysis procedures, and they can not reflect continually changing vulnerabilities and threats information of individual network system on real time. For this reason, this paper suggests new system design methodology which shows a scheme to collects and analyzes data from network intrusion detection system and vulnerability analysis system and estimate quantitative risk levels. Additionally, experimental performance of proposed system is shown.