Large-scale integration of intermittent energy has brought many problems to active power dispatching of the power grid, which will not only increase the operation cost, but also increase the operation risk. This paper developed a multi-time scale scheduling strategy, integrated day-ahead scheduling, intra-day dispatching and automatic generation control (AGC) system, in order to ensure the safe and stable operation of power grid. The strategy aims to minimize the sum of operating costs of power system, and sets six constraints such as power flow constraint, to analyse and optimize the dispatching process of power systems. After simulation and analysis by Particle Swarm Optimization (PSO) algorithm, the results show that the strategy has a significant optimization on the power system with intermittent energy.