Abstract: By using the classical lamination theory (CLT) and considering the coupling effect of tension and bending, an analytical model of stiffness prediction was developed for composite laminates with in-plane waviness. The influence of the parameters associated with in-plane waviness such as the waviness ration, the fiber off-axis angle and the waviness position on the 3D stiffness of the laminates was investigated quantitatively. It is found that the theoretical predictions agree well with the results in literature. And the longitudinal elastic modulus, the transverse elastic modulus, the in-plane shear modulus, the major Poisson's ratio, and the in-plane bending stiffness are greatly affected by the waviness defect. The approach established provides a procedure to evaluate the effects of waviness defect on the mechanical properties of composite laminates.