Abstract: Production rules is a knowledge representation applied in numerous fields presently.In expert system for confirming structure of biomass soft-sensor hybrid model in fermentation process，when adding new rule into rule-base，exist of redundancy affects reasoning efficiency and reasoning veracity.A detecting redundancy method for rule-based in the expert system is introduced in this paper.Distinguish of redundancy，disposal of redundancy and realization of redundancy verification are presented.Experiment shows that，the detecting redundancy method can judge whether rule added is redundant according to inputting conditions and existent rules，and can debase complexity of model when avoiding effect of redundancy to reasoning efficiency，which favors to optimize structure of hybrid model.