Abstract: The concept of deductive system was proposed on formula set F(S) of BL propositional logic system, and the strong congruence relation was introduced. We discussed the connection between deductive systems and strong congruence relations in BL system, gave the method of interconversion between them, and obtained the reducibility of interconversion between them.

Key words: deductive system, strong congruence relation, fuzzy logic, propositional logic system BL