This thesis studies and develops an agent-based on-line monitoring and diagnosis system. With the advent of industry facilities toward high speed and automation, the on-line monitoring and diagnosis mechanism becomes important. The traditional time-based maintenance strategy cannot consider all practical conditions of machines. The accidental breakdowns may occur unexpectedly. In order to make production line automation, yield high production rate, and enhance the ability of market competition, an effective way is to ensure facilities running smoothly and to reduce the manpower monitoring. Meanwhile in order to reduce the cost of development and enhance the feature of reuse, we use a communication interface to integrate and interact information among developed softwares. Through this system, users may easily monitor and diagnose the machines on production lines through user interfaces, such as display of machine status, malfunction alarming, trend chart, waveform, spectrum, cepstrum and envelop spectrum, etc. A model consisting of domain knowledge and behaviors of cooperative multi-agents to integrate various facilities and functions in different production lines is proposed. In addition, via a Web-based environment, it releases the restrictions by of temporal and regional isolation. The system provides a real-time and dynamical operation circumstance and can meet the needs of different levels of users. Consequently, it is of greatly help to lower the cost of personnel and enhance the ability of market competition.