Based on the practical operation of diesel engine fault and a lot of professional experience and knowledge, an improved gray target engine fault diagnosis model was proposed. The ault sign standard model structure was built by Fault-to-date statistical data and professional experience and knowledge,and multi-target heart Failure was constructed. The causes of a diesel engine was diagnosed through the fault symptoms and the cause of the malfunction bull's-eye from all sort and its practicability and validity have been indicated by its result.