Abstract: In order to make use of large-scale space end-effector's grapple performance farthest, this paper gets fixed grapple tolerance of end-effector from the perspective of optimization design, other than from the perspective of traditional mechanism design. According to end-effector's working procedure and principle, the grapple tolerance is divided into two parts: capture tolerance and retract tolerance. Through analyzing structural factors influencing large-scale end-effector's grapple tolerance, capture and retract tolerance optimization models are developed respectively. The optimized grapple tolerance (128.58mm, 128.58mm, 100mm, 15.12°, 15.12°, 16.32°)^T is acquired based on linear weighting method and penalty function method. Finally, some experiments about grapple tolerance optimization and grapple performance are conducted by utilizing simulation technology. Experiment results show that mathematical optimization models proposed are reasonable and the optimization algorithm is right.