Abstract: In order to predict the low-velocity impact characteristics of composite laminates, a simulation method for impacting delamination response was proposed based on spring-mass model. First, the changes of flexural rigidity and deflection before and after delamination were calculated according to the presupposed delamination number and delamination area, therefore the time histories of tup motions with the delamination event was simulated. Then, contact force was calculated by the acceleration of tup, and the permanent indentation depth was calculated based on the elasto-plastic contact law of material. Whereafter, the low-velocity impact experiment was carried out on the panel of co-curing composite wing box, and the impact sites were divided into three types: the mid-point position of the skin between two spars, the boundary of the T joint bonding area of skin and spar, and the point just over the spar. After that, the characterstics of contact force, delamination threshold force and indentation depth of different impact sites were contrasted and analyzed. Finally, the contact force, permanent indentation depth and absorbed energy of impact site of the 1st type were calculated by the proposed model, as well as the influences of length-width ratio of rectangle plate on the membrane stiffness and contact force were also analyzed. The results show that the simulated contact force is well agreed with the measured result, and the accuracy of simulations for permanent indentation depth and absorbed energy are also acceptable, thus the proposed model is available. The membrane stiffness increases rapidly with the length-width ratio decreasing, thereby promotes the contact force increase significantly.