Reactive power optimization is very important to power systems economic operation and nowadays, the research about it gets more and more popular. The paper presents a reactive power optimization algorithm of particle swarm optimization combined with sensitivity analysis. The paper first builds the mathematic model of reactive power optimization and introduces particle swarm optimization. Then, presents the sensitivity method in detail and talks about the process of computing the sensitivity. Finally, take the algorithm into practical application and the results proves that sensitivity analysis could improve the particle swarm optimization algorithm.