Abstract: Output Predictive PI(OPPI) is a new method used in process control. The PI (Predictive PI) and OPPI methods are introduced briefly. A new OPPI method based on analysis of B-spline is presented. This method analyses discrete curve and predicts output of the process controlled with three-order B-spline function, and carries out PI control with the predictive output. The results of its simulation and application used in tube-typed furnace and constant-temperature trough are given. It is simple,reliable, easy to realize, and is suitable for temperature control and other objects with slow time-varying feature.