Abstract: A mathematical model for stiffness reduction of circular composite laminate with delaminations after low velocity impact based on spring-mass model was presented. Plate was divided into a delaminated portion of central disk and an undamaged portion of annulus plate. Bending theory and classical lamination theory were used to obtain the displacement of the plate to compute the stiffness. A FE model for laminate with delaminations on ABAQUS was established to validate the analytical model. Drop weight impact test was conducted and C-scan results was used to calculate the stiffness. The reduction result was used in spring-mass model predicting the contact force history. Comparisons of FE simulation and experiment test results show good agreement of the stiffness reduction and the prediction of contact force history. This analytical method can be applied to low velocity impact analysis with delamination damage.