Based on an inverse piezoelectric inchworm motor researched and manufactured before,the influence of balanced stiffness of a clamping body with triangulation amplification on its output displacement and the performance of motor was researched.The research results show that rotary displacement is resulted by non-balanced stiffness of the clamping body and the horizontal displacement is reduced also.Then because the rotary displacement and the performance of the inchworm motor are lower,the extent of releasing guide is reduced.For overcomming this problems,a method to balance the equivalent extent stiffness in two sides of a piezoelectric stack was proposed by adding a piece of metal board,and the dimension of the board was calculated by Finite Element Method(FEM).After adding a metal board,it demonstrates that the horizontal displacement and response frequency of the clamping body are increased and the guide is approximate to be fully released.The performance of the inchworm motor is advanced dramatically.After balancing the stiffness,the response frequency is 450 Hz,the highest driving force is 7 N and the highest velocity is 1.49 mm/s.