The fix platform and the move platform of the parallel mechanism with 3SPS+PS are linked with four chains at the corner of the platform, the mechanism model and kinematics model is established, the force Jacobi matrix is obtained. According to the relation of kinematics Jacobi matrix and force jacobian matrix, the duality of the force jacobian matrix is deduced. The load and the position of the load are given, the mechanical model is established, the analysis is conducted when the load changes at the positon with the changes of 0-360 degrees, and then force of the four prismatic pairs are derived, and using MATLAB software to draw out the performance charts. The results of the analysis are important to the structure design and strength analysis.