Under conditions of without considering the stiffness of joint driving device itself, respectively, in 2PRR parallel mechanism connecting rod within the plane of the three typical locations along the X and Z to step loading, measurements were obtained in the corresponding direction displacement value. Stiffiness curves in different directions and locations were given, and the measured displacement and the displacement analytic values calcaulated by boundary element method were compared. The results show that in the same measuring point, the stiffness of Z is significantly greater than the stiffness of X. At the different measuring points, although the specific direction stiffness changed, but it is in the same order of magnitude. The relative stiffness value of the real test and the theory stiffness values of boundary element calculation have the same variation trend.