For the stability analysis problem of a T-S fuzzy system, a membership functions integration-based method is proposed to relax the existing conservatism. Firstly, indefinite integral functions are derived for the membership functions. Then with a piecewise linear approximation approach, the membership functions and their integration functions are involved in a fuzzy-like Lyapunov function-based stability analysis process. Finally, comparisons with existing methods are presented in the simulation section to show the advantages of the proposed method.