Analysis　of　how　to　extract　medical　diagnosis　rules　from　medical　cases.　Based　on　the　rough　set　theory,　a　way　of　acquiring　knowledge　is　introduced.　Using　this　theory,　we　analyze　the　data,　propose　some　possible　rules　and　reveal　an　optimized　probability　formula.　The　steps　of　implementation,　which　includes　the　continual　information　discretization　system,　information　reduction　system,　decision　acquirement　rules,　decision　model　generation,　etc.,　are　explained　through　case　study.　In　the　end,　the　whole　process　of　knowledge　acquirement　is　discussed,　which　can　effectively　solve　the　choke　point　problem　of　acquiring　knowledge　in　the　expert　system.　At　the　same　time,　it　also　provides　a　new　way　to　solve　the　application　of　artificial　intelligence　technology　in　the　field　of　medicinal　diagnosis.　©2005　IEEE.