Abstract: Based on the analysis of wear particles of diesel engine, a pattern recognition method of the wear mode of diesel engine was originally put forth, by combining rough sets theory and fuzzy theory. Thus the knowledge representation system is reduced, the weight coefficients are calculated according to rough sets theory, then the membership function is chosen based on fuzzy theory, and finally some interested conclusions are given with respect to some examples. It has been found that the calculation concerning the pattern recognition of the wear modes of diesel engine is effectively simplified by adoption of rough sets theory, while the pattern recognition reliability of the wear modes is increased effectively by use of fuzzy theory.