The invention relates to a suspension type gear speed reducer. The suspension type gear speed reducer comprises a cabinet body, an input gear shaft, an intermediate shaft gear, an intermediate gear shaft, an output gear, and an output hollow shaft, wherein backstops are respectively connected to two ends of the intermediate gear shaft; each backstop comprises a housing, a shaft guard ring, a cover plate, a star wheel, springs, lifting pins and pin rollers; each star wheel is connected to the intermediate gear shaft through a key; each housing is connected to the outer part of the corresponding star wheel in a sleeving manner; two sides of the outer wall of each star wheel are connected with the corresponding cover plate in a limiting manner through the corresponding shaft guard ring to encapsulate a cavity between the star wheel and the corresponding housing; in each cavity, a plurality of star wheel bosses in clearance fit with the inner wall of the corresponding housing are arranged at the periphery of the corresponding steel wheel; a wedge-shaped cavity is formed among each star wheel boss, the corresponding star wheel and the corresponding housing; each pin roller which is axially parallel to the intermediate gear shaft is arranged in the corresponding wedge-shaped cavity; a pin hole facing each pin roller is formed in the wall of the corresponding star wheel boss wall on one side of the corresponding wedge-shaped cavity; and each spring is arranged in the corresponding pin hole, so that each lifting pin is connected to the pin hole in a penetrating manner, and the state that the corresponding pin roller is tightly pressed to be limited in the inner wall of the corresponding housing and the corresponding wedge-shaped cavity is generated.