Abstract: Nonlinear instability associated with composite laminates with a delamination under dynamic loads wasstudied. A dynamic instability equation , called Methieu equation , considering the nonlinear elastic and dampingeffect s , was deduced and the corresponding solution in terms of analytical expressions was obtained on the basis ofReddy’s simple higher order shear deformation theory and the delaminnation model developed by the authors. Thedynamic instability of the parameter vibration was investigated. From some typical examples , it is clear that theeffect s of delamination lengths and locations on the natural frequency , buckling load and instability regions , and theeffect of excitation f requency of dynamic load on the amplitude of the first parameter vibration are significant . Theinfluence of linear and nonlinear damping on the maximum deepness of“t raction”is discussed. Some typical examples indicate that the dynamic instability behavior of the laminates gradually decreases with increasing delamination ;especially , when delamination is close to the mid-plane of the laminates , the influence of delamination on the dynamic instability behavior of the laminates is most remarkably.