Power companies’ bidding strategy is a doubleoptimization problem, the top of the ISO model is to ensure the maximization of social and public benefits,which is to determine the participation of the electricity generating companies. The second layer is the largest profit model of power generating companies. Using a simple heuristic algorithm, the optimal solution is overall, and has nothing to do with the initial selection. In this paper, an improved use of the Particle Swarm Optimization (PSO) for the largest profit optimization problem is made, and the deterministic method and the results are  compared. On the IEEE30 sixnode system,the effectiveness of the method is verified.