A hi-quality website is crucial to a company for a successful e-business. The technique maintainers are always faced with the problem how to locate the prime factors which affect the quality of the websites. In view of the complexity and fuzziness of BtoC website, a quality diagnosis method based on the multi-attribute and multi-layer fuzzy comprehensive evaluation model including all the quality factors is proposed. A simple example of diagnosis on a famous domestic BtoC websites shows the specific steps of this method and proves its validity. The process of quality evaluation and diagnosis system is illustrated and the computer program of diagnosis is given.