Proper maintenance scheduling of equipment can keep high availability of power system, avoid the damage of failure and reduce the waste of cost. In the authors' research, facing up to the difficulty of short of data for maintenance scheduling in the electric power industry, element availabilities with various kinds of maintenance intervals can be calculated by the dimensional reduction method. Considering the system availability, maintenance scheduling of equipment can be optimized by element maintenance interval adjustment. In this paper, sacrificing system availability within allowance and keeping system availability during the process of optimizing maintenance scheduling was discussed in detail. There effectiveness was verified by the proper maintenance scheduling for the electrical elements of thermal power stations.