The invention discloses a telescopic steel structure folding ladder. The telescopic steel structure folding ladder comprises a ladder frame body, wherein an inverted-V shape structure is lapped by a left ladder frame and a right ladder frame of the ladder frame body, and transverse treading rods are arranged in the ladder frame body; a rotating fixing mechanism is arranged on the ladder body and is provided with a gear shaft, a gear, a bearing, a blocking piece, the ladder frame body is provided with a telescopic mechanism which is provided with a sliding groove, limiting holes, a sliding frame, a supporting rod, a sliding block, a stop block, locating holes, a goods placing box, a limiting column and a telescopic connecting shaft; supporting mechanisms are arranged below the sliding frame, and each supporting mechanism is provided with supporting legs, a fixed shaft, rolling bearings, a supporting table, a round hole, a round opening and a rubber pad; and an auxiliary mechanism is arranged on the sliding frame and is provided with a rectangular clamping groove, a toolbox, a rectangular clamping buckle, a universal wheel, a driven wheel, a threaded hole, a threaded rod, a handle and a clamping-connecting piece. The telescopic steel structure folding ladder has the beneficial effects of being simple in structure and high in practicability.