It is complex to simulate the system with continue controlled object and discrete controller, in order to avoid the complexity, a new method to describe the continue controlled object of internal combustion engine with discrete model was given, which is based on the principle of the total energy of an isolated system is constant and the theory of heat transfer in the cylinder, for the internal combustion engine has the special cycle of operation. In the paper, an example of ethanol-gasoline internal combustion engine was given to prove the modeling way is feasible. The digital fuzzy PID controller is design and the simulation results show that the controller is workable. The discrete model will be used in digital controller design and simulation for the fuel supplying control.