Based on the minimum principle of reserve cost, operating cost and environmental cost, an environmental/economic dispatch model is constructed in this paper. The improved particle swarm optimization algorithm with time-varying acceleration coefficient is used to solving the model. Through the example simulation, the results show that the built model can make the optimization of the microgrid more reasonable. It can effectively reduce the reserve cost, the operating cost and the environmental cost. This is a good exploration of the environmental/ economic dispatch for microgrids.