Operating times constraint of discrete control equipment results in a space-time close coupled problem in dynamic reactive power optimization. A new method is proposed to assign the operating time of equipment properly so as to achieve the optimization as a whole. The method determines preliminary operating table of equipment by static reactive power optimization results and operating constraints， which indicates whether an equipment is allowed to operate or not. Optimization is carried out with the operation allowable equipments in the researched period. With the optimization results of that period and operating constraints in the whole day， the operating table of subsequent periods can be renewed and decoupling of 24 periods can be realized as well. The new method is not only simple in modeling， but also easy in implementation. Test results have shown that it can reduce daily power loss and meet the needs of real-time operation within allowable daily operating times.