Abstract: The safety of take-off and landing of ship-based helicopter is seriously affected by ship swaying motions. Unfortunately, it's difficult to find a mechanism in existing parallel mechanisms, which not only can bear heavy load but also has large workspace. In order to assist helicopter landing safely, a large-scale mechanism for ship-based stabilizing platform is presented. Based on kinematics model, a theory of axis optimization is presented for the large-scale parallel mechanism. The method is applied to multi-objective optimization design of guideway axis arrangement, where the actuators' performance indices such as displacement, velocity, and acceleration are chosen as objective functions. Based on equivalent transformation of supporting rod’s motion, the axis and angles of the revolute joints are optimized. The numerical examples show that the kinematics performance of the platform is effectively improved by the theory of axis optimization, and the theoretical basis is provided for mechanism synthesis and manufacturing of the large-scale ship-based stabilizing platform.