Abstract: The objective of this research is to develop a diesel engine governing characteristics model for the hardware-in-the-loop (HIL) simulation study of tractor system. The model is used to control an electric motor so that it produces torque-speed characteristics closely matching those of a diesel engine. A set of curve functions are added to construct the diesel engine governing characteristics that is a continuous function of the governor control position variable and the engine speed variable in the engine operating range. By comparing the simulation and experimental results, it is showed that the model could represent engine static and dynamic governing characteristics. The continuity and simple function structure is of benefit to the controller design and real-time implementation.