The invention discloses a gear finish machining device used for solving the problem that gear machining precision is not high. The gear finish machining device comprises a box body, a first gear shaft fixing and adjusting assembly and a second gear shaft locating assembly. Oil liquid and grinding material mixture are contained in an inner cavity of the box body. The two ends of a first gear shaft are fixed in the first gear shaft fixing and adjusting assembly through bearings. The first gear shaft fixing and adjusting assembly comprises bearing cover plates, the bearings, sliding bearing seats, sealing gaskets, locating screws, and a spring jack beam mechanism. The second gear shaft locating assembly comprises bearing assemblies, gaskets and bearing end covers. The two side walls of the box body are provided with shaft holes. The bearing assemblies, the gaskets and the bearing end covers are sequentially fixed on the sides walls, where the shaft holes are located, of the box body. According to the gear finish machining device and method, a gear is contacted with grinding materials, the generating cutting principle is adopted for grinding machining, and the surface roughness Ra value at least can reach the surface precision of 0.01 nanometer.