The invention provides an auxiliary measuring tool for a third-gear and fourth-gear synchronizer gear ring assembly of a six-gear transmission of a front-drive passenger car. By the adoption of the auxiliary measuring tool, the labor intensity is lowered. A locating groove matched with supporting feet on a third-gear and fourth-gear synchronizer intermediate ring is formed in the periphery of a base. The outer circular face of a mandrel disc is in clearance fit with the inner circular face of a third-gear and fourth-gear synchronizer inner gear ring. The lower ends of two support pillars are connected with a base plate, and the upper ends of the two support pillars are connected with a support. An upper bushing is connected with the support, and a lower bushing is connected with a pressing disc. A connection portion of rapid clamping tongs is in clearance fit with a longitudinal assembling hole formed in a mounting base, and the lower end of the rapid clamping tongs extends into a connecting hole in the upper bushing and is connected with the upper end of a pressing shaft in a vertically-movable manner. The lower end of the pressing shaft extends out of the lower end of a connecting hole in the lower bushing and is provided with a nut. The upper end and the lower end of the pressing shaft are in micro-clearance fit with connecting holes in the corresponding bushings. A spring is wound around the pressing shaft, and the upper end and the lower end of the spring are correspondingly in elastic contact with the two bushings. The upper ends and the lower ends of three pressing heads are correspondingly connected with the pressing disc and the large end face of a third-gear and fourth-gear synchronizer outer gear ring.