The invention relates to the technical field of immersed tube tunnel construction, and particularly relates to an internal formwork system of the immersed tube tunnel. An inner side formwork and an inner side formwork support used for supporting the inner side formwork are arranged. The inner side formwork support comprises a fixed part and a movable part, the movable part is hinged to the fixed part, the inner side formwork comprises an upper formwork body and a middle formwork body which can form an integral structure, the upper formwork body is arranged on the outer side of the fixed part,and the middle formwork body is arranged on the outer side of the movable part. After poured concrete is solidified into immersed tube sections, the middle formwork body is separated from the immersedtube sections by driving the movable part to rotate; the fixed part is arranged on a fixing frame with a lifting mechanism, and the upper formwork body is separated from the immersed tube sections bydriving the lifting mechanism to descend. The structure is used for replacing traditional manual formwork removal, after the first immersed tube section is completed, a formwork does not need to be supported, disassembled or reassembled for subsequent immersed tube sections of the same shape, the problem that in immersed tube concrete pouring, an inner side formwork cannot be subjected to telescopic formwork removal is solved, the construction time is shortened, and the construction cost is reduced.