ANN is a method of short_term load forecasting which has been researched the most recently. This paper proposes a new load forecasting model based on Particle Swarm Optimization（PSO）．PSO is a novel random optimization method which has extensive capability of global optimization．PSO is used to optimize the weighting factor of Radial Basis Function（RBF）neural network and the optimal model is applied to forecast load．The application of ANN in combination forecasting has been summarized.