This paper aims at the parametric drive train design, modeling and performance simulation of a parallel diesel hybrid electric bus(PHEB). AVL/CRUISE and MATLAB/SIMULINK are used for modeling and simulation. The simulation tasks include fuel consumption calculation over the typical city bus drive cycle of China, maximum velocity calculation and acceleration time calculation. Based on the simulation results, a comparative analysis is performed on the portion of fuel consumption in the internal combustion engine consumption map. The simulation shows that the engine operates in a more efficient condition in the hybrid electric bus than that in the conventional bus. Thanks to the hybrid electric drive train system, both fuel economy and traction performance of the bus are enhanced in a considerable step. The simulation analysis fits test results on road and chassis dynamometer well.