A transient model of off-road vehicle powertrain has been established according to the basic laws of thermodynamics and heat transfer. With the utilization of distributed simulation system based on high level architecture (HLA), the transient simulation of powertrain has been executed. A cycle experiment on a off-road vehicle has been designed and conducted, and the models have been verified by the experiment data. Using the method founded, the conditions of energy distribution and engine heat statistics have been discussed. Other additional mechanical loads (i.e. fan, pump etc.) were taken into account in this model as well. The analyzed results show that the model can reflect the dynamic characteristic of the powertrain more accurately. Furthermore, it is approved that the integrated approach is available for off-road vehicle powertrain simulation.