The invention discloses a novel fastening structure for a through belt of a low-speed diesel engine. The novel fastening structure penetrates through and is in fastening connection to a machine base,a rack and a gas cylinder body, and comprises the through bolt, a positioning sleeve, a positioning screw, a positioning block, a hydraulic nut and a positioning nut, wherein an upper fixed through hole and a middle fixed through hole are formed in the gas cylinder body; a through hole is formed in the rack; the machine base is equipped with a lower fixed through hole and a transverse mounting hole; the transverse mounting hole and the lower fixed through hole define inverted-T-shaped penetration; the upper fixed through hole is embedded into the positioning block, the positioning nut is arranged in the transverse mounting hole, the through bolt and the positioning sleeve which are integrally welded pass through the positioning block, the middle fixed through hole, the through hole and thelower fixed through hole; the positioning sleeve is in matched positioning with the lower fixed through hole; the positioning screw jacks the positioning sleeve; the hydraulic nut and the positioningnut are separately connected to the upper end and the lower end of the through bolt; and a hydraulic elongator is used for fastening the hydraulic nut, the positioning nut and a through bolt pump forconnecting the machine base, the rack and the gas cylinder based in a fastening mode. The novel fastening structure is simple, is good in performance, is high in reliability, is convenient in mounting and dismounting, and avoids the risk that machine base scrap is caused by damages on a threaded hole.