Abstract: Fuzzy Petri net is a ideal tool for fuzzy production knowledge representation and reasoning.This paper designed the FPN model for fuzzy production rule-based knowledge base and implemented a backward fuzzy reasoning algorithm based on FPN througn the recursive.The algorithm was verified by examples in this paper.Using the algorithm,one can calculate the tokens of any appointed places which correspond to the true fuzzy values of the relevant propositions.The algorithm is strong in logic expressionan easy to implement in computer sustem.The proposed algorithm can effiectively reduce the computing space through transforming a large and comples system based on FPN into a small subsystem relating to the problems and improve the computational efficiency.

Key words: FPN,DSS,Knowledge representation