PVC reactor is a typical chemical process which has complex system with unknown dynamics. It is well known that this plant is controlled by PID control. The PID controller is well understood and accepted among operators and engineers due to its intuitive simplicity. However, it is seen difficult to find useful PID gains for complex systems. On the other hand, many control techniques have been proposed in order to improve controlled performances for this plant. Since these techniques are too complex, they may be difficult to apply to actual plants. In this paper, we propose GPC method which has PID control structures. Here, this design method includes the constrained parameter tuning method to assure positive PID gain. Also, we define and design operating parameters which influences controlled performance. Finally, we show the simulation results of PVC system that is controlled with PID gains obtained by GPC algorithm.