The invention discloses a method for correcting a C-shaped steel casting. The method comprises the following steps: preparing a steel plate according to the dimensions of a C-shaped steel casting to be corrected, fixedly welding a fixing block on the steel plate, enabling a mounting hole to be formed in the fixing block in the length direction, mounting a rotating shaft in the two ends of the mounting hole through first bearings, enabling two threaded sections with equal lengths and opposite spiral directions to be formed on the rotating shaft, mounting a threaded sleeve on each of the two threaded sections, and further arranging an arc-shaped preheating pipe used for heating the steel casting at the arc top on the inner side of the C-shaped steel casting. The method for correcting the C-shaped steel casting has the benefits as follows: large-sized correcting auxiliary equipment does not need to be used, the operation is simple, easy to carry out, safe and reliable, the C-shaped steelcasting is corrected from the two ends simultaneously, the correcting time is shortened, the correcting efficiency is higher, and the two ends are corrected simultaneously so as to ensure the consistency of the correcting forces borne by the steel casting at the two ends; besides, the dimensional welding repair quantity of the casting due to deformation is greatly reduced, the welding cost is saved, and the production cycle of the casting is shortened.