Abstract: In this paper the behaviour of buckling and postbuckling of composite hat-stiffened panels of aircraft wings under compression was investigated experimentlly and analytically. In tests the critical instability load was measured and examined carefully. According to the test results, two methods for experimentlly determining the critical instability load are presented, and the postbuckling stresses distribution and buckling mode of the skin are discribed.The critical instability load is calculated by "Finite Strip-Element Method", and the numerical results are in good agreement with test data.The effect the lateral support conditions on the stability of the panels is analized and the analytical method is discussed and improved.