Abstract: Based on the microst ructure model established by the authors , coinciding with the actual configuration ofbraided composites , a model to predict the elastic properties was proposed by using the 3D FEM , coupled with theperiodical boundary conditions. The calculated values by the model well agree with the measured values. Numericalresult s verify the effectiveness of the model. The st ress and st rain fields of the model under such typical load casesas tension and shear were analyzed in detail , respectively. The result s indicate that the application of the periodicalboundary conditions guarantees the continuities of the t raction and displacement on the parallel boundary surfaces ofthe cubic model. Therefore , the st ress field and the st rain field obtained by the model are more reasonable than bythe existing FEM models.