Abstract: To improve the collaboration quality between human and robot,a gravity balance method for cobot(collaborative robot) is investigated to alleviate gravity burden on human operator.A spring system is introduced to realize gravity balance of an articulated robot in a motion range as large as possible.The stiffness and original distortion are specifically designed so that the spring system can modulate appropriately the spring force along with motion of the robot to realize self-balance within a large range.The design is tested in some points within the motion range of the robot,and the residual gravity moment is one to ten percent of the original moment.The result shows that this method can realize gravity balance to some degree.