The microgrid has become a helpful supplement to the traditional power system because of its various clean resources and flexible power supply. Exclusive researches on microgrid operation are required as it is different from traditional power system operation. The load distribution optimization in microgrid is given special attention to make the total power generation cost minimum by optimizing the power generated by each micro-source while satisfying the constraints on system operation. A mathematical model is developed for load distribution optimization in a microgrid consisting of a photovoltaic system， a micro-turbine， and an energy storage system. The numerical solution based on particle swarm optimization（PSO） is worked out and an illustrative system is calculated with the algorithm proposed.