Aiming at a series of requirements of obstacle avoidance trajectory planning of manipulators, a new algorithm based on six-order polynomial trajectory planning is proposed. Firstly, the six-order polynomial is used for the trajectory planning of the manipulator. Assuming that the coefficients of the sixth order term in the curve equation are undetermined parameters, by adjusting these parameters, the shape of the curve can be changed to make manipulators avoid the obstacle and to optimize performance indicators of the trajectory simultaneously. Thus, the obstacle avoidance trajectory planning of manipulators is transformed into a multi-objective optimization problem. Secondly, combining collision detection results and kinematics indexes, a fitness function is defined by the weighting coefficient method. At last, an ideal collision-free trajectory that is collaborative optimized in kinematics, trajectory length and rotation angle is planned in the joint space through genetic algorithm optimization. Additionally, the algorithm is validated by simulation experiments with MATLAB, the results show that the method of this study can effectively plan obstacle-free trajectories satisfying the performance requirements of the manipulator.