To configure the capacitor-type blocking devices at the neutral point of a transformer can be taken as an optimization problem.In this paper,a computing model of the power grid with blocking devices is designed.Then,based on the characteristics of capacitors,a mathematic model for optimal configuration is constructed by taking small device number and small sum of neutral point currents as the objectives.In the mathematical model,the particle swarm optimization algorithm is combined to cut off as much device cost as possible without affecting the blocking efficiency,thus achieving the best blocking effect at the cost of the least blocking devices.Finally,the method to solve the computing model is discussed,and an improved optimization algorithm is proposed and then proved to be effective by an example.