As most of the present decision methods of propositional formulas are based on semantics and cannot give an important reference in many reasoning applications,namely deduction procedure,a deduction-based decision method that can give the deduction procedure during the decision procedure is presented based on the propositional calculus system L.

By means of theory of truth degrees of formulas,according to deduction theorems and completeness theorems,the new concepts of porlar index and consistency degrees for general theories in Lukasiewicz propositional fuzzy logic systems are introduced.

Having studied the formal deductive system L~* for fuzzy propositional calculus, and investigated the fuzzy deduction theorem of L~* system in detail.