Computers and the information they process are critical to many organizations' ability to perform their mission and business functions. It therefore makes sense that executives view computer security as a management issue and seek to protect their data which are stored in these computers. Presents a main objective of introducing a modeling design and verification of the monitoring part of common intrusion detection framework (CIDF) using Petri Nets. To enhance the security of a system by monitoring system activity and detecting a typical behavior, statistical unusual behavior must be found in the observation of the system. Such a monitoring system will be capable of detecting intrusion that could not be detected by any other means. These systems that do collect audit data are the only way to build a real secure system which is the most important part of the network. Presents a proposed model of the monitoring part of the CIDF based on Petri Nets modeling technique. Tests the proposed model using the Petri Nets properties.