The parallel mechanism of 4-SPS was studied. 2T2R (2 translational and 2 rotational) 4-DOFs (degrees of freedom) parallel mechanism were obtained by configuration evolution of adding and altering the follower-limb. The constraint condition of solving the position and attitude workspace about 4-SPxyz S/PxPzUxz parallel mechanism was built. The set of points was used to calculate dimensional size of workspace. The concept of sensitivity was introduced. The numerical method was used to calculate dimensional size of position workspace and scope of attitude workspace in the solution of different scale.