The invention relates to a tunnel middle partition wall structure and a method for staged excavation of a tunnel by means of a middle partition wall method. One side of a tunnel primary support (4) isattached and fixed to a tunnel surrounding rock, and secondary lining is attached to the other side of the tunnel primary support (4); a first erect middle partition wall (1) and a second erect middle partition wall (2) are vertically arranged in the tunnel in parallel, and both the upper ends and the lower ends of the first erect middle partition wall (1) and the second erect middle partition wall (2) are connected with the tunnel primary support (4) separately; a cross partition wall (3) crosses with the first erect middle partition wall (1) and the second erect middle partition wall (2) and is transversely arranged in the tunnel, and both the left end and the right end of the cross partition wall (3) are connected with the tunnel primary support (4). Compared with a traditional middlepartition wall method, stress on the middle partition wall is rational, instable failure of the whole is unlikely to occur, and connection failure does not occur; a sufficient support effect on a vault can be achieved, so that vault settlement is effectively controlled. Moreover, the whole construction process of the middle partition wall is simplified, lots of manpower, material resources and time are saved, the construction progress is accelerated, and the total construction cost is reduced.