Operation of the gun/turret system in a military tank is limited by several constraints some of which are posed by obstacles existing on the vehicle's own platform. In this study we tried to eliminate some of these constraints by the design and adaptation of transmission system between the chassis of the vehicle and the upper structure. The proposed approach is to adapt a motion platform on the top of the chassis of the vehicle. The motion platform chosen is a 3RPS parallel robot will achieve persistent control by allowing the upper structure of the vehicle to always back to the horizontal position and stay in a level position, in spate of the displacements and vibrations on the vehicle. The design of the chassis of the vehicle and the parallel platform is made using SolidWorks Computer Aided Design software. After that according to structural characteristics of the 3-RPS parallel robot, the mathematical model of the posture inverse kinematics is established. Based on Matlab software, SimMechanics, the simulation model of this robot is established. The validity of the inverse kinematics is proved by comparing the two models. And during the simulation, the related kinetics data and motion animate are obtained. Finally the simulation comparison after setting the parameters of the PID controller is established too, the animation shows that the control effect is obvious where the moving platform follows the desired trajectory.