In the background of condition-based maintenance, the equipment in a certain state could choose different maintenance levels, which have different impacts on maintenance time, maintenance costs and the improvement of equipment state, which will in turn affect the time schedule of equipment maintenance. Therefore, both the maintenance mode and the maintenance time are viewed as decision variables of making maintenance schedules. Based on the method of risk assessment, the overall risk of grid operation and the revenue of equipment maintenance are defined. Furthermore, since the single risk indicator for the final decision is not comprehensive. And the maintenance results of single optimization model have different impacts on the economy of equipment maintenance and the reliability of equipment after maintenance. Therefore a joint optimization model integrating the overall risk of grid operation and the revenue of equipment maintenance is established. Then the three maintenance schedules are compared to analyze the maintenance effects on equipment reliability and economy. The result of application verifies the validity of the method.