Abstract: In order to effectively increase the load carrying capacity of free-floating space robot, a multi-constrained multi-objective trajectory optimization method based on MOPSO (multi-objective particle swarm optimization) algorithm is proposed. Combined with the established dynamics model of space robot system under load carrying condition, load maximization is transformed into the multi-constrained multi-objective trajectory planning problem which simultaneously satisfy minimization of joint torque, base disturbances and system energy. The corresponding mathematical model of MOP (multi-objective optimization problem) is established. The Pareto solution set meeting the requirements of load maximization is solved by MOPSO algorithm which tackles constraint conditions effectively. By simulation, the availiablity of this method is proved.