The invention provides a diesel engine fuel oil fuel oil system fault pre-diagnosing method based on a gray model. The method comprises the steps of: firstly, detecting fuel oil system operation parameters at regular intervals; secondly, utilizing a gray prediction model GM (1, 1) to analyze the deterioration trends of the fuel oil system operation parameters, utilizing predicted data sequences to describe the current performance state of the fuel oil system, and constructing a fuel oil system state to-be-detected model; then establishing a fuel oil system fault reference model, and utilizing a standardization method to carry out initial value image processing on operation parameters in the to-be-detected model and the reference model; and finally, utilizing a gray association degree model to detect a gray association degree between the system to-be-detected model and the fault reference model, and according to a maximum association degree rule, recognizing the current fault type of the fuel oil system. According to the invention, in the deterioration initial phase of the fuel oil system, the current fault type can be accurately identified by the method, maintenance personnel are guided for carrying out prevention maintenance on a diesel engine, the diesel engine is ensure to operate under the optimal working state, and the reliability and the economy of the equipment are improved.