Abstract: On the basis of expansion of management information base and protocol data unit of simple network management protocol , a net monitor system for application software was designed and implemented . The system played a monitoring role for the member variable and function of the class in the applying procedure . The mode of exchange and transmission of monitoring information between management station and management agent was studied , including definition of protocol stack , design of communication protocol , etc . When monitoring information transmitted , the necessity of grouping and regrouping of datagram was illustrated , algorithms of grouping and regrouping were designed . The results show that the exact and timely exchange and transmission of monitoring information are attained from management agent to management station .