A transient, six-cylinder diesel engine model for cold test has been developed for analyzing the engine fault through the engine torque curve. The model is based on physically working cycle, thermodynamic theory and dynamics mechanism. The simulation of this model, implemented on Matlab/Simulink, can not only achieve engine faults detection before hot test, but also indicate different causes of engine faults, such as initial phase change, intake valve closing-time delay, and so on. It is shown that the diesel engine model for cold test proves its significance to improving cold test technology.