By logical diagnosis and fault tree analysis, the operational condition of 300 diesel engines was analysed and a fault tree model of diesel engines under hazard condition was established. The occurence probability of hazard condition at the current level was determined to be 0.000288. Structural importance and probable importance of the model were proPosed statistically and qualitical improvements of governor design, manufacture and installation were suggested to reduce inefficiency occurence probability. Through calculation and comParison of crucial importances, the key importance for risk condition occurence was ascertained to be improper maintenance, adjustmemt and service of fuel injection PumP. The effects of other failures were determined.