Abstract: The evolution of delamination is studied by usingdouble-linear characteristic model of damage. With a representation ofdamage parameters for elastic/shear moduli, a series of differentialequations of damage parameters with respect to strain are derived, and therelations of cracking dissipated work with respect to damage parameters arealso obtained. By computing the evolution of strain, strain rate and damageparameters in a certain interface of composite laminates under impact withvariety of initial velocities, delamination in the interface and its effectto shear moduli are yielded. Then the delamination regions between the firstand the second layer after impact are evaluated by checking whether one ofdamage parameters is changed at each point in interface. The result showsthat the shear moduli start to decay in the point where shear stress reachesthe shear strength. The decaying amplitude increases as the initial impactvelocity of iron ball being raised, while it decreases outwards from theimpact point nearby. With all boundaries simply supported, the delaminationregion appears firstly in the center of one interface, and they expand asthe initial impact velocity being raised. Several independent delaminationregions will appear along two symmetric axes of interface plane between thefirst and the second layer of composite laminates if the initial impactvelocity is higher enough.