The invention belongs to the technical field of gear transmission gearboxes, and particularly relates to a three-speed gear transmission gearbox with a gear striking preventing function. The three-speed gear transmission gearbox with the gear striking preventing function comprises an output shaft, a clamping mechanism, a first fixing ring, a shifting rod, a first fixing plate, a supporting mechanism, a first guide block, a second guide block, a third guide block, a fixing housing, an input shaft, a first connecting barrel, a second fixing ring, a fixing block, a third fixing ring, etc., wherein a storing chamber is formed in the fixing housing; a through fixing circular hole is formed in the side surface of the storing chamber; a through moving groove is formed in the side surface, opposite to the fixing circular hole, of the storing chamber; two first guide grooves are symmetrically formed in the outer circle surface of the input shaft; and two third guide grooves are symmetrically formed in the outer circle surface of the input shaft. According to the gear transmission gearbox, when a gear which rotates at a slow speed is forcibly embedded into a gear which rotates at a high speed, or when the gear which rotates at the high speed is forcibly embedded into the gear which rotates at a slow speed, the problem of gear striking in the gearbox can be avoided.