Due　to　the　difficulty　of　knowledge　accessing　in　traditional　gear-box　intelligent　diagnosis　system,　a　diagnosis　technology　based　on　CBR　(Case-based　Reasoning)　and　RBR　(Rule-based　Reasoning)　hybrid　method　was　proposed　in　this　paper.　On　the　basis　of　analyzing　the　advantages　and　disadvantages　of　the　two　methods,　the　combination　of　the　reasoning　technologies　was　utilized　in　fault　diagnosis　of　gearbox　of　rolling　mills.　As　a　result,　the　accuracy　and　efficiency　of　fault　diagnosis　were　improved　greatly.　Due　to　the　shortage　in　similarity　algorithm　in　traditional　retrieval,　a　new　case　retrieval　algorithm　was　proposed.　Therefore,　the　problem　of　inaccuracy　in　traditional　similarity　algorithm　was　solved　effectively.