A big challenge of designing and implementing a monitoring system for distributed systems such as the Computational Grid is how to quickly and dynamically deploy and manage a large collection of monitoring sensors. Currently available monitoring systems often use the static sensor deployment mechanism, which makes the sensor deployment quite difficult and inefficient. We have developed an agent-based grid monitoring system that enables fast, dynamic, and ondemand sensor deployment and management. The monitoring system perfectly solves the problem of fast and dynamic sensor deployment using dynamic sensor loading mechanism. In addition, the monitoring system uses software agent technology to solve the problem of dynamic and on-demand sensor management.