Currently, PID controllers have been widely used in industrial control. And computer control systems are widely used in the field environment. How to design a discrete PID controller which has a good control performance is very important for existing control objects. In this paper, particle swarm optimization and quadratic performance index are used to optimize the control parameters of the discrete PID controller. The optimized results are given at last. By simulation studies and analysis, the optimal parameters of the PID controller are found by particle swarm optimization algorithm, and the quadratic performance index has a good effect on optimal control.