Aiming at the problem that the existing 2R1T (two rotations and one translation) vehicle engine motion simulation platform mechanism cannot realistically simulate the motion state of the engine due to the parasitic motion. In this paper, the geometric relationship between the restraint force of the branch and the rotation axis of the 2R1T parallel mechanism(PM) is analyzed. A construction criterion of the branch for redundant mechanism without parasitic motion is proposed. From the perspective of mechanism innovation design, a novel 2-RPS/2-UPS/PS PM with large bearing capacity without parasitic motion is designed. This paper solves the problem that the existing 2R1T PM without parasitic motion cannot be applied to the occasion of large load. The kinematics analysis of the mechanism is carried out, and the characteristic of the mechanism without parasitic motion is verified. The workspace of the mechanism is calculated. And the kinematics simulation analysis, stress analysis and prototype experiment of the mechanism are carried out. The correctness of the design index of the motion simulation platform and the characteristic of the mechanism without parasitic motion is proved. It provides a theoretical basis for the application of the mechanism without parasitic motion in large load-bearing occasions.