Abstract: The stiffness of the parallel mechanism is an important indicator to judge the institutional performance. The 3-PRS parallel mechanism is taken as an example to propose a stiffness solving analysis method based on orthogonal experiment and regression analysis. An orthogonal array of the platform radius and rod structure parameters is established by orthogonal experiment method based on a kinematics model and finite element model. Multiple experiments are calculated using ANSYS-Workbench, then a variety of polynomial regression models are established according to the stiffness of the finite element analysis of experimental data, and the best regression model can be selected under the principle of the smaller the residual standard deviation is, the better the degree of the regression function fitting will be, and verified with the MINITAB software. The results furnish a new type of method for stiffness properties of parallel mechanism study and achieve the law of influence of different factors on the stiffness utilizing this stiffness regression function model.