Myhill-Nerode theorem describes an important characteristic of regular languages,it is a classical and elegant result in finite automata theory. In order to extend Myhill-Nerode theorem,states transition semigroup on a finite automaton M and M-semigroup on Σ are introduced,their some properties are discussed. The equivalence relation in Myhill-Nerode theorem is generalized,a new characteristic of regular languages is given based on the states transition semigroup and the M-semigroup,then Myhill-Nerode theor...