In recent years, power saving problem has become more and more important in many fields and attracted a lot of research interests. In this paper, the authors consider the power saving problem in the virtualized computing system. Since there are multiple objectives in the system as well as many factors influencing the objectives, the problem is complex and hard. The authors will formulate the problem as an optimization problem of power consumption with a prior requirement on performance, which is taken as the response time in the paper. To solve the problem, the authors design the adaptive controller based on least-square self-tuning regulator to dynamically regulate the computing resource so as to track a given reasonable reference performance and then minimize the power consumption using the tracking result supplied by the controller at each time. Simulation is implemented based on the data collected from real machines and the time delay of turning on/off the machine is included in the process. The results show that this method based on adaptive control theory can save power consumption greatly with satisfying the performance requirement at the same time, thus it is suitable and effective to solve the problem.