Abstract: In this paper, an new composite PID control and its stepwise design method are developed for one order unstable processes with time delay. Firstly a proportional controller is designed to stabilie the unstable processes. Then a two-stage PID controller is designed to optimie the response of the whole composite control system, in which a new set of tuning formulas for the two-order stable processes with time delay is used. Simulation results show the advantage of the whole control algorithm.