The invention discloses a bearing assembly all-in-one machine and an assembly method thereof. The assembling of bearing balls and press-fitting of a bearing retainer are important processes in the assembly of rolling bearings. The machine comprises an operating platen, a ball loading module, a retainer pressing-in module, a station switching mechanism and a base, wherein the ball loading module comprises an inner ring triaxial mechanical arm, a ball triaxial mechanical arm, an inner ring mounting chuck and a ball blowing mechanism; the retainer pressing-in module comprises a pressing-down mechanism and a retainer pushing mechanism; the ball blowing mechanism comprises an air pressure ball bin, an on-off valve, a nozzle and a ball conveying pipe; and the retainer pushing mechanism comprisesa feeding device seat, a feeding air cylinder, a return spring, a T-shaped locking pin, a feeding bottom plate, a feeding device, a feeding inclined rail and a retainer storage bin. By matching the station switching mechanism, the ball loading module and the retainer pressing-in module, the assembly of an inner ring, an outer ring, the balls and the retainer of the bearing can be completed fullyautomatically, and the assembly precision and uniformity of the bearing are effectively guaranteed.