Abstract: A homogenization-based mechanical model for predicting the viscoelastic properties of composite materials with periodic microstructures was presented. The viscoelastic properties of fiber bundles and 3D 4-directional braided composites were obtained using this model and the finite element method, respectively. Based on the numerical results, the variation of viscoelastic properties with process parameters was presented. The results show that with the increasing of braided angles, the viscoelastic properties in the braided direction increase, and with the increasing of fiber volume fractions, the viscoelastic properties in the braided direction decrease, which agree well with the experiment results.