Servin et al proposed a 2-step temp oral phase unwrapping algorithm,which only needs 2extreme phase-maps to achieve exactly the same results as the standard temporal unw rapping method.But this method also has some problems.In order to optimize the range of sensitivity coefficient G and improve the measuremen t accuracy,an improved temporal phase unwrapping algorithm is proposed in this paper,which is an extension of Servin′s method.F irst,we add an intermediate sensitivity fringe pattern,project the fringe patterns with different sensitivities onto the object surface,and then co llect the deformed fringe patterns with a CCD camera.Then we obtain the unwrapped phase with larger sensitivity coefficient G by cascading the sensi tivity coefficients.We derive the initial phase conditions of the 2-step temporal phase unwrapping algorithm.Finally,the experimental eva luation is conducted to prove the validity of the proposed method.The results are compared with those of the method in Ref.[21] .The experimental results show that this method can achieve high sensitivity,and the results are more accurate.