Aimed at the difficulty of disease diagnosis caused by the weakness of information receptivity of local farmer in our country, a diagnosis system for cucumber disease was designed based on website. Users just need to check similar symptoms, but not to face to numbers in diagnosing process, that means to simplify the general information that expert systems need. This system used production as the knowledge representation method, and adopted quantitative diagnosis combining with rulebased reasoning (RBR) as reasoning mechanism, the results accuracy was judged by its credibility and uniqueness by numbers of symptoms related with diseases. The efficiency of quantitative diagnosis was improved by RBR.