According to the nonlinearity of the temperature of polyvinyl chloride (PVC) polymerization reactors, a generalized predictive control (GPC) algorithm based on piecewise affine is proposed. Firstly, a dynamic equation for the polymerizing temperature is derived in accordance with the heat-balance mechanism. The piecewise affine model is based on the polymerizing temperature and conversion rate. The state space of each subsystem is described by an oval set. Next, LMI is used to design the controller and set up the Lyapunov function to analyze the system stability. Finally, the proposed piecewise affine model is applied to the generalized predictive control algorithm. Simulation and industrial application results show the validity and feasibility of the proposed strategy.