The invention relates to a vertical roller gap calibrating method. The method comprises following steps: according to the central line of a vertical roller inlet rack roller and the central line of a vertical roller outlet rack roller, the rolling central line is determined; the measuring roller gap of an operation side vertical roller is measured, that is, the shortest distance between the rolling central line and the operation side vertical roller is obtained; and the measuring roller gap of a drive side vertical roller is measured, that is, the shortest distance between the rolling central line and the drive side vertical roller is obtained. According to the measuring roller gap of the operation side vertical roller, the measuring roller gap of the drive side vertical roller and the calibrating formula, a calibration roller gap of the operation side vertical roller after the vertical roller is replaced and a calibration roller gap of the drive side vertical roller after the vertical roller is replaced are determined; and according to the vertical roller gap calibrating method, calibration is accurate, the method is easy, time is saved, the human intervention factor can be reduced, the product quality can be obviously improved, and the large camber capable of generating the width and the vertical roller area is avoided.