For the shortcomings of the traditional performance diagnosis method of power plant boiler current, the paper proposed a method of introducing the fuzzy comprehensive evaluation into performance diagnosis of power plant boiler. This method first took the boiler safety, economy and environmental protection three aspects into account to find boiler performance parameters. In order to accurately understand all aspects of boiler performance, it used two fuzzy comprehensive evaluation; Then it combined the fuzzy theory and reality to establish the membership function of each performance parameter; Ultimately, it not only judged the overall performance of the boiler, and made a reasonable judge on safety, economy and environmental protection. This evaluation method makes the boiler operators have a thorough understanding of Boiler performance. It's a very good guide for the real-time evaluation of boiler performance and the diagnosis of potential problems in running process.