Compliant mechanism becomes a promising alternative to the traditional ones for precision applications. Flexure hinge compliant mechanisms have been used in different fields. However, the design of their geometric parameters is so critical. Therefore, a lot of work are done in optimization of their design parameters. One of the main important steps is to select the sensitive parameters in such design problems. In this article a study of sensitivity of geometric parameters of positioning stage compliant mechanism are represented to be used as a pilot step for the selection of the optimization design variables. The effect of each parameter is regarding to the achieved amplification ratio of the positioning stage and the input stiffness of the mechanism. The modeling is done using Pseudo Rigid Body Model on MATLAB. The sensitivity analysis is done using ISIGTH software. The results of different sensitivity analysis methods reveal the most important parameters of the compliant mechanism that have significant effect on the amplification ratio.