Abstract: Composite laminates are often regarded as homogeneous anisotropic plates in practical engineering structure design, and the stiffness of laminates is characterized by equivalent elastic modulus. In order to characterize the elastic properties of composite laminates, the relationship between engineering constant and stiffness coefficient of the single-layer material, the equivalent elastic modulus of 0/90_S orthogonal symmetrical laminates, the equivalent elastic modulus of quasi-isotropic laminates and the effect of stacking sequence on the equivalent elastic modulus of symmetrical laminates are studied by theoretical calculation and ANSYS ACP simulation. It is fount out that there is a simple correspondence between the single-layer engineering elastic constant and stiffness coefficient. The equivalent elastic modulus of 0/90_S orthogonal symmetric laminates is about half of the sum of single-layer on-axis engineering constants E_L and E_T on the main directions. The equivalent elastic modulus of the quasi-isotropic laminate is about one-third of the sum E_L and E_T on the main directions. The equivalent elastic modulus of laminated plate does not change after changing the ply drop order, but the ply drop order has a great influence on the bending stiffness of laminated plate. The rationality of the finite element method is verified by the theoretical calculation. This study can provide theoretical and simulation guidance for the application design of composite laminates.