A new solid unit cell model is developed based on the microstructure analysis of three-dimensional (3D) six-directional braided composite (6DBC) produced by four-step 1 x 1 procedures in this research. First, the volume control method is applied to analyze the spatial movement traces of yarns. Then the microstructure configuration and squeezing condition of yarns is analyzed in detail by the mathematical modeling. The relationships between the microstructure parameters of unit cell and the braiding process parameters are derived. The parametrical solid unit cell model for modeling the microstructure of 6DBC is established. Finally, the main microstructure parameters of specimens are calculated to validate the effectiveness of the model. The predicted results agree well with the available experimental data. In addition, the squeezing conditions of the braiding yarns and the axial yarns are analyzed in detail, respectively. The variations of the key microstructure parameters with the braiding angle are discussed. Results indicate that the parametrical unit cell model has provided a better understanding of the relationship between the microstructure and the braiding process parameters for 3D 6DBC.