The widespread networks in campus provide students with rich resources, but they also provide unhealthy information which may have negative effects on students. Filtering systems have been developed to prevent web users from unhealthy web contents. However, the false positive and false negative rates of those tools are still high and thus need to be improved. In this paper, we propose an Internet behavior monitoring method by integrating the BHO plug-in techniques with URL-based filtering technique, and apply this method in the campus network. Designed in the client/server mode, the method has the capabilities of filtering out unhealthy websites according to the given black list, and can record the students' online web activities into XML documents and/or pictures. The recorded contents can be replayed by the campus network administrators. This method assists teachers to keep eyes on students' learning state, and notifies the administrators to react immediately to help campus web users correct their inappropriate behaviors.