The invention discloses a synchronous assembling device comprising a servo base. The servo base is a device for driving a servo transition tool unit and is used for rapidly fixing and positioning a product in a transition tool. A rotation base is fixed to the base. Grippers which can rotate to the position of the servo transition tool and are used for fixing a one-way bearing are arranged on the rotation base. A push rod which is used for pushing a transmission piece of the servo transition tool to the one-way bearing is arranged on one side of a sliding base. The grippers used for grabbing the one-way bearing are arranged at the two ends of the rotation base correspondingly, feeding is conducted through one end, the other end is connected with a transmission fixing base in a butt joint manner, a transmission piece in the transmission piece fixing base is pushed into a clamping groove of the one-way bearing connected with the transmission piece fixing base in the butt joint manner through the push rod, and assembling is completed; and during feeding, the feeding angle is detected through an industrial camera and fed back to a control system, a servo motor is driven to control a rotating shaft to rotate, the feeding angle is regulated to the required feeding angle, it is ensured that the later-period pushing process of the transmission piece can be smoothly completed, and the assembling quality is ensured.