The invention relates to a self-limiting mechanical supporting rod which comprises an upper supporting assembly, a lower supporting assembly and a return spring. The upper supporting assembly comprises an upper support, an upper inner supporting rod, a lower outer supporting rod, an upper pin shaft is erected on the upper support, both the upper inner supporting rod and the upper outer supporting rod are movably connected to the upper pin shaft, an opening is formed in the other end of the upper outer supporting rod in an inclined mode, an outer chamfer is arranged at the end of the opening, and one end of the return spring is connected to the upper pin shaft; the lower supporting assembly comprises a lower support, a lower inner supporting rod and a lower outer supporting rod, a lower pin shaft is arranged on the lower support, both the lower inner supporting rod and the lower outer supporting rod are movably connected to the lower pin shaft, the lower outer supporting rod is located on the outer side, and the outer end of the lower outer supporting rod is provided with an inner chamfer corresponding to the outer chamfer; the lower inner supporting rod is inserted into a tube hole in the upper inner supporting rod, the lower outer supporting rod is inserted into an annular gap between the upper outer supporting rod and the upper inner supporting rod, and the other end of the return spring is connected with the lower pin shaft. The problem that supporting space of an existing supporting rod is limited is effectively solved.