Abstract: A geometrical model for 2D 1×1 and 2×2 biaxial braided composites was proposed. The jamming condition and the cross-sectional variation of the yarns were considered. Based on the microstructure and volume-averaged method, an analytical model was established to predict the elastic properties of 2D biaxial braided composites. Numerical results show good agreement with the experiment data, which validated the effectiveness of the model. The influences of various parameters such as braid angle, fiber volume fraction and cross-sectional shape of yarns on the effective elastic constants were also studied. The results indicate that the braid angle has a complimentary effect on the elastic constant; the effective modulus is in proportion to fiber volume fraction; cross-sectional shapes of yarns have slight effects on the elastic constant.