With the rapid advances in Internet and Grid technique, an increasing number of applications will involve computing systems. These applications in turn create an increasing demand for efficient resource management, request handling policies and admission control. In this paper, we propose an efficient admission control algorithm to protect the critical resource of server and improve the performance of the computing system. Stability of CPU utilization is aimed to protect the server from overload and under-load. It is then beneficial to keep a satisfactory response time of requests, high throughput and less potential loss of service. We analyze the stability in detail and present a method for tuning control gains in order to guarantee the system stability. Finally, we perform simulations to evaluate the performance of the proposed algorithm. Simulation results demonstrate that the proposed algorithm stabilizes the utilization of CPU in the computing system if the control gains are appr...