The invention provides a clamping method for clamping a rolling mill rack of a clamp of a hydraulic jacking device. The clamping method comprises the following steps: establishing models of clamps ofthe rolling mill rack and the hydraulic jacking device; assembling the two models, confirming a clamping module according to a gap between the models and processing the clamping module; putting the clamping module in a corresponding position when the clamps of the rolling mill rack and the hydraulic jacking device are assembled, and clamping the rolling mill rack by the clamp of the hydraulic jacking device. The gap between the clamps of the rolling mill rack and the hydraulic jacking device assembled is confirmed by means of the models of the clamps of the rolling mill rack and the hydraulicjacking device to design and process the corresponding clamping module, so that when the clamps of the rolling mill rack and the hydraulic jacking device are assembled, the clamping forces between theclamps and the rolling mill rack are ensured by plugging the clamping modules in a corresponding gap position between the clamps of the rolling mill rack and the hydraulic jacking device, and therefore, the clamps of the rolling mill rack and the hydraulic jacking device are connected tightly.