Abstract: Following the geometric pattern of the constituent yarn systems in 3D woven structures, a general purpose geometric cell model is developed. The length and orientation angle of the constituent yarns in each yarn system within a unit cell are calculated, and then the fiber volume fraction of 3D woven composites can be obtained. To verify the geometric model, samples of 3D woven composites with 11 various binding patterns are selected and the fiber volume fraction is measured. Experiment results are in good agreement with the outcomes of the model. Further, the geometrical model is used to discuss the effects of the binding pattern on the fiber volume fraction and yarn's orientation angle. It shows that a layer-to-layer binding can offer a higher degree of fiber volume fraction than a through-thickness binding, and that binders of an orthogonal interlock binding have a greater orientation angle than that of an angle interlock, indicating a more efficient reinforcement in the thickness direction of 3D woven composites.