The invention discloses a method and system for determining and controlling roller bending force of roller change of a rolling mill, and relates to the technical field of maintenance of steel rollingequipment. The roller weight of a to-be-changed roller of the target rolling mill, the friction force of a roller change rail and the bearing block weight of the to-be-changed roller are acquired; thetheoretical minimum roller bending force needed by lifting the to-be-changed roller is determined based on the roller weight, the friction force of the roller change rail and the bearing block seat of the to-be-changed roller; and the theoretical minimum roller bending force is applied to the to-be-changed roller, the roller bending force at a preset roller bending force gradient value is cumulatively applied on the basis of the theoretical minimum roller bending force until the rail level of the roller change rail and a roller change vehicle in a rack where the to-be-change roller is locatedis reached, and the target roller bending force is determined. The technical problem that as the roller bending force of an existing roller change method is excessive, oil leakage of a hydraulic cylinder of the rack frequently happens is solved.