Abstract: A new method for calculating viscoelastic damping and energy loss of fiber composites is presented. Firstly, on the scale of lamina, the energy dissipation formula is obtained by using a damping matrix and the theory of linear anisotropic viscoelasticity. Then on the scale of laminate, an effective damping(loss) matrix is obtained by using an equivalent energy theory (including stored energy and dissipated energy). In terms of the effective damping matrix, the energy loss and specific damping of the laminate can be calculated by using the effective stress and effective strain. The key point is the derivation of the effective damping matrix, which is a function of damping coefficients, volume fraction, and stiffness coefficients of each lamina and the effective stiffness coefficients of the laminate. In this way, the energy loss of fiber composites under arbitrary loading can be computed, which is very important in the numerical analysis for viscoelastic material and structures. In the end, several numerical examples are given to show the reasonability of the model.