The invention relates to a diesel engine lubricating system fault diagnosis method based on the Bayes network. According to the method, fault types and external symptoms of a lubricating system are abstracted into fault layer nodes and symptom layer nodes, and a diesel engine lubricating system Bayes network model is established; performance parameters of the diesel engine lubricating system are detected by utilizing a data acquisition system, a linear proportion transformation method is employed to carry out classification processing on the performance parameters, and the actual work state information of the lubricating system is acquired; a Hugin combined tree algorithm is employed to convert a corrected lubricating system Bayes network model into a combined tree. Before inference diagnosis, on the basis of the actual work state of the lubricating system, through resetting the prior probability of the fault layer nodes, adaptability correction on the Bayes network model is carried out, so the actual work state of the lubricating system can be accurately described through the model, nondeterminacy of model inference is reduced, and thereby fault diagnosis accuracy is improved.