A 3-DOF parallel 3-PRS mechanism, which can realize one translational and two rotational motions and also can brace the secondary mirror used in laser beam focusing, was proposed. Traditional Euler angle for describing the motion of moving platform was adopted, and based on that, kinematic model of a 3-DOF mini mechanism was built to analyze its direct and inverse kinematics performances including Jacobian matrix generation and solving the problem of accompanying motions. Furthermore, qualitative analysis of singularity and quantitative analysis of the reachable workspace of the mechanism were given. By combining ADAMS with MATLAB, the maximum and minimum motions of the moving platform including the motions of rotational x axis, rotational y axis and along z axis were approximate 15.167 1°, 13.319 4° and 9.954 1 mm respectively. The derived results strongly prove that a 3-DOF mini mechanism can fulfill the design requirement of the supporting structure of supporting the secondary mirror using laser beam focusing.