The invention provides a method for prolonging the service life of a synchronizer of a gearbox of a commercial vehicle. The method aims at a gear shifting air cylinder with the synchronizer. Firstly,reasonable synchronizer locking tooth impact force is calculated through a specific formula, and the internal structure of the gear shifting air cylinder is subjected to throttling design according tothe locking tooth impact force. By means of the design, the service life of the synchronizer can be remarkably prolonged, and gear shifting force, down-shifting force and gear shifting time of the gearbox cannot be affected.