The invention relates to the manufacturing field of undersea tunnel immersed tubes, in particular to a device and method for synchronously lifting a steel reinforcement cage in the tunnel immersed tube manufacturing process. The device comprises a plurality of air sacs, air sac base plates and an air compressor, the air sac base plates are arranged on the upper surfaces of the air sacs, and the air compressor is respectively communicated with the air sacs thorough pipes. The method includes the steps that firstly, after the steel reinforcement cage is pushed by a sliding rail to be in place, the air sacs with the air sac base plates are installed on the lower portion of the steel reinforcement cage; then air is inflated into the air sacs by the air compressor through the pipes, and when the steel reinforcement cage is lifted to reach the set height, air inflation is stopped; finally, after the sliding rail is disassembled, the air sacs slowly exhaust air through an air exhaust valve, a supporting column arranged on the air sac base plates is stressed, and then the air sacs are taken out. According to the device and method for synchronously lifting the steel reinforcement cage, the air sacs are inflated to lift the steel reinforcement cage, the steel reinforcement cage stably operates, and the height of the steel reinforcement cage can be accurately controlled. The device is simple in structure, and cost can be saved compared with existing hydraulic and pneumatic mechanical devices.