In order to solve the problem that the standard of GB/T 7607—2010 is not referential enough in the health status assessment of diesel oil in service,a comprehensive degradation value model was established based on the health status assessment technology in PHM theory.Based on the statistics of monitoring data and laboratory experience,the corresponding relationship between the comprehensive degradation value and the health status of diesel engine oil in service was graded.According to the three principles of monotony,correlation and predictability,the evaluation indexes of diesel oil health status in service were selected,and the normalization methods of various indexes were given.The weight of each index was determined by entropy weight method,a formula for calculating the comprehensive degradation value of in-service diesel oil was established,and the comprehensive degradation value of each sample data was calculated.The reliability of the method was verified by comparing the characteristic peaks of antioxidants in the infrared spectra of the samples with different comprehensive degradation values.