Abstract: In order to establish the quantitative relationship between the damage index and delamination damage parameters for accurately quantitative monitoring delamintaion damage on stiffened composite panel, a quantitative monitoring method based on surrogate model was proposed. The initial samples acquired by impact experiment were used to construct polynomial surrogate model via the interpolation algorithm to represent the quantitative relationship between the delamination damage parameters and damage index. The quantitative monitoring process of delamination damage was that probability-based diagnostic imaging algorithm was used to localize the delamination damage and to acquire the relative distance and damage index, then the damage area was optimized by the polynomial surrogate model based on damage index and relative distance. The validity of the proposed quantitative monitoring method was assessed by quantitative monitoring damages at different locations with different areas on a stiffened composite panel. The experiment results show that the proposed method can quantity identify the damage of stiffened compo-site panel accurately. The error of damage location is below 6%, and the error of damage area is below 5%.