Provided is an arm-supporting structure, including a front arm connector, a rear arm connector, an adjusting means for an upper support and a lower support, and an elastic supporting means. The front arm connector, the upper support, the rear arm connector and the lower support are articulated sequentially to form a parallelogram structure. The upper end and the lower end of the adjusting means are articulated with the upper support and the lower support, respectively. Two ends of the elastic supporting means are connected with the adjusting means and the upper support, respectively. The elastic supporting means has a length that is elastically stretchable. The adjusting means automatically adjusts its position in accordance with the swinging of the upper support and the lower support, shifts the position of the fulcrum of the elastic supporting means, and automatically reaches a balance of force.