Abstract: To solve the problems such as the insufficiency of the required data and the low credibility in reliability prediction for diesel engine in engineering, this paper utilizes the property of fuzzy number which is suitable for quantifying fuzzy information and combines the fuzzy sets and the traditional similar product method by using fuzzy sets theory and interval analysis. Then it puts forward a new reliability prediction method which combines the fuzzy similar product method and the fuzzy comprehensive evaluation, which is then used to do the fuzzy prediction on the reliability of the diesel engine's air compressor. This method not only makes sufficient use of the reliability data of the old machine type, but also combines the experts' practical experiences and judgments. It realizes the mutual complement of the fixed information and the uncertain information. This method has the practical value in engineering.