The invention relates to a final assembly system and a final assembly method for segmented products. The final assembly system comprises a horizontal rack trolley, an installing rack trolley and a butt joint rack trolley. The installing rack trolley is provided with a first six-freedom-degree supporting table and a supporting frame fixed to the first six-freedom-degree supporting table. The firstsix-freedom-degree supporting table is provided with a first posture detection device, a second posture detection device, a first tracking device and a second tracking device. A pushing device is arranged on the upper side of the supporting frame, and a front filling clamp and a rear filling clamp are correspondingly arranged on the front side and the rear side of the pushing device. The pushing device is provided with a first gap detection device and a second gap detection device. The butt joint rack trolley is provided with a second six-freedom-degree supporting table and a support frame fixed to the second six-freedom-degree supporting table, and the second six-freedom-degree supporting table is provided with a third posture detection device and a third tracking device. The final assembly system has the beneficial effects that the integrity is high, the automation degree is high, and centering precision is high. The final assembly method has the beneficial effects that the logic isreasonable, the executing efficiency is high, and safety and reliability are achieved.