The invention provides a climbing supporting mechanism having expansion and automatic meshing functions, and a construction method of the climbing supporting mechanism. The supporting mechanism comprises a supporting frame, a climbing upright post, a lifting device and a hydraulic system; a telescopic device capable of sliding in the horizontal direction is arranged on the supporting frame; the telescopic device comprises a sliding component, a hang claw box body, a transverse movement driving component and a telescopic bracket; the sliding component is located on the contact surface between the telescopic bracket and a beam of the supporting frame; the transverse movement driving component is supported on the beam of the supporting frame; and the outer end of the telescopic bracket is connected with the hang claw box body. An automatic meshing device is composed of a hang boot, a hang claw and a rebounding component; the hang boot is welded on a bearing element of a vertical structure to form a bearing key; the hang claw is meshed with the hang boot; the hang claw is connected on the hang claw body by a hinge shaft; and the rebounding component is connected at the rear end of the hang claw. The supporting mechanism provided by the invention has the automatic meshing and expansion functions, thus the supporting mechanism is convenient to use, the labor force is saved, the cost is reduced, the efficiency is improved, and the construction safety is ensured; in this way, the supporting mechanism can be widely applied to the ascending supporting of the large wall-attached structures or apparatuses.