Abstract: An improved three-cell model,which includes interior cells,two kinds of surface cells and corner cells,was proposed based on the geometrical characteristic of the yarns for 3-D 4-directional braided composite.The variation of characteristics for the yarns in the cells was considered in the present model.The average yarn packing factor was proposed to distinguish the different cross-sectional variations of the yarns in different cells.Based on this model,the stiffness prediction model was established with the method of stiffness averaging.By comparing with the available experimental data,it shows the applicability of the present model.At last,the influence of the braiding angle and the fiber volume fraction is discussed.