When the unstable complex system employs PID to control, as the manual regulation of parameters, it does not only time-consuming but also cannot guarantee the best performance; as a result it is hard to achieve good controlling effect. Basing on the advantages of particle swarm algorithm, this paper puts forward the controlling strategy of utilizing particle swarm algorithm to optimize PID parameters. It provides the controlling model and principle of particle swarm optimizing PID parameters, as well as doing simulation analysis on several unstable complex systems. When input provides a unit s...