The utility model discloses a permanent expansion joint water stop structure, which comprises a water stop elastic body, wherein the water stop elastic body is arranged between expansion joints on concrete lining layers of a tunnel, and can be in an annular structure, in addition, the cross section of the water stop elastic body is in a rectangular shape, and in addition, a hollow water stop cavity is arranged inside the water stop elastic body. The inner wall of the water stop elastic body and the inner wall of the concrete lining layer are positioned in the same plane. Pressure media can be filled in the water stop cavity, so the compressible water stop elastic body is placed between the expansion joints, when the concrete lining layers in the tunnel contract, the expansion joints become wide, the water stop elastic body expands, the expansion joints are enabled to be always sealed, and the water leakage of the tunne cannot be caused. During the installation, the water stop elastic body can be simply and conveniently arranged in the expansion joints.