The invention provides a steam turbine expansion difference control structure and method. The steam turbine expansion difference control structure comprises rotors and cylinder bodies arranged outside the rotors in a sleeving manner; and the rotors rotate around the axis. The expansion difference control structure comprises at least one fixing piece; each fixing piece and the axial section of the corresponding cylinder body are connected through a connecting structure; the axial section of each cylinder body is further provided with at least one expansion difference monitoring device which is connected with an information processing and controlling unit; and the information processing and controlling unit controls the connecting structures to act. By means of the steam turbine expansion difference control structure and method, each cylinder can be made to have a relative dead point, it is guaranteed that the expansion differences of the cylinders do no affect one another or be accumulated, each cylinder is only affected by the expansion difference between the corresponding rotor and the corresponding cylinder body, and the expansion differences of the cylinders are made to be maintained at a low level all the time; and meanwhile, the expansion difference control structure can be adjusted, and the problem that automatic restoration cannot be achieved in the prior art is solved.