The invention discloses a steel belt defect grading method and system based on a surface inspection instrument. The method comprises the steps of obtaining the actual defect data from the surface inspection instrument, determining a defect name Am, determining a defect type Bn in the defect name, dividing a defect level Cp, setting a defect parameter E, wherein the defect parameter emnp representsa division reference value corresponding to the pth defect grade of the nth defect type in the mth defect name, and the defect parameter E is a positive real number, determining a comparison parameter F, wherein the comparison parameter is greater than, equal to, less than, equal to or less than a parameter, combining the comparison parameter with the defect parameter to obtain a grading rule matrix Y which comprises the numerical value intervals corresponding to different defect grades, and comparing the actual defect data with the grading rule matrix to determine the defect grade. Accordingto the steel belt defect grading method and system based on the surface inspection instrument, the product defect recognition and upgrading can be automatically completed, and the quality inspectionefficiency and the precision are improved.