The intake manifold model of turbo charge engine is constructed and a high speed calculation algorithm is developed for model based predictive control in real time. The model is built from the analysis of its thermodynamic and hydrodynamic characters and the sampled experiment data which are expressed by a set of differential equations with switching (bifurcation) on the right hand side. The switching surface is divided into two parts: sliding and crossing. We analyze the reasons of error existing on the surface, and develop well-defined control semantics for managing behavior discontinuities in the case of state transition. The calculation algorithm can seamlessly integrate the continuous behavior generation and the discrete mode switching. Using this method we can solve this model under the entire region of input throttle angles. Furthermore, the stability is greatly improved and the calculation time is greatly reduced for the real time control system.