Built-in rolling bearing fixing structure

The invention provides a built-in rolling bearing fixing structure which comprises a gear shaft, an output shaft, a united ball bearing and a first spacer ring; the gear shaft is of a hollow structure, the united ball bearing is mounted on the output shaft, the output shaft and the united ball bearing are both coaxially arranged in the gear shaft, and the first spacer ring abuts against one end of the united ball bearing and is fixedly mounted on the inner wall of the gear shaft. The first spacer ring is effectively utilized, by changing the size of the inner hole of the first spacer ring, the first spacer ring can block a first inner ring and prevent the first inner ring from moving along with the output shaft, the number of parts and the space size are not increased, the purpose that the bearing is not damaged when the bearing is disassembled can be achieved, meanwhile, the parts are convenient to grind, high precision is guaranteed favourably, and the built-in rolling bearing fixing structure is suitable f