Knowledge acquisition is the bottleneck in developing expert system．It usually takes a long period to acquire disease knowledge using the traditional methods．Aiming at this problem，the paper presents the relationship between rough sets and rule-based rapeseed disease knowledge，namely the application of rough sets in knowledge acquisition from rapeseed disease expert．Then the exclusive rules，inclusive rules and disease images of rapeseed disease are built based on the RHINOS diagnosis model，and the definition of probability rule is put forward．At last，the paper presents the rule-based automated induction reasoning method，including exhaustive search，post-processing procedure，estimation for statistic test and the bootstrap and resampling methods．The results of experiment show that rough sets not only are a good framework for knowledge acquirement，but also Can accurately induct the rules of plant diseases．This method Can act as the assistant tool for development of diagnosis expert system，and has a extensive application in intelligent agriculture information systems．