Abstract:First, the viscoelastic properties of 3D braided composites are obtained using the homogenization method and the FEM, and variation of thermal expansion coefficients with time is studied based on the numerical results of relaxation moduli of materials. The influence of braided structures and processing parameters (braided angles、fiber volume fractions) on initial thermal expansion coefficients is presented, and the numerical results agree well with the experimental data. The research work in the paper furnishes the basis for further investigating the thermo-viscoelastic properties of 3D braided composites.