Abstract: Aimed at solving the contradiction between the need of large diameter condensation structure for Space Power System and the limitation of the current carrying capacity, a deployable mechanism for the secondary mirror support was designed, based on a two-mirror off-axis condensation system. The major configuration of the deployment mechanism was made of a three-link serial mechanism, with two parallel four-bar mechanisms, which can deploy in the horizontal and vertical directions separately, and ensure that the secondary mirror component remains translational movement during the mechanism deployment. Kinematics equation of deployment was deduced, and the work space was solved to plan the scheme of the mechanism deployment. The position precision and attitude accuracy of the deployment was studied, and the sensitivity of structure parameters was given. Finally, the virtual prototype of the mechanism was built with ADAMS software, and the deployment was simulated to verify the correctness and rationality of the design.