Abstract: For a class of controlled plants that can be approximately described as a first order model with pure time-lag, a set of optimal expressions based on the characteristic parameters of the controlled plant are proposed by way of parameter optimizing, data fitting and so forth to tune the parameters of PID controller. Testing results indicated that the PID control system designed in this way has such good characteristics as short adjusting time, small overturning and small static error especially the dynamic characteristics which are more excellent than from any other empirical Formulae. In addition, its control effect will remain unchanged even if the ratio of pure time-lag to time constant of the controlled plant is big. Being simple and easy to implement, the approach proposed will not only solve the problem that the tuning effect on conventional PID parameters is improper but also provide a sound foundation for building further a self-adaptive PID control system based on the latent process parameter.