Abstract: A sort of hexahedral microstructure unit-cell (MUC) geometric model is presented,whose performances are variable, aimed at resolving the troubles of the mechanical analysis about the gradient characteristics in the tubular and 3D braided composites components. The microstructure of MUC is diverse in multifarious 3D braided composites. Finding out the rules of the MUC geometric diversifications and the changed trends of its yarns volume fraction along with its coordinates,a feasible analysis model is provided for making certain the relationships among these factors and local mechanical performances in the MUC.A geometrical model was constituted for a kind of tubular 3D braided composites, of which the symmetrical axes are straight. The function relationships among the parameters were demonstrated in detail. The model about rectangular 3D braided composites preform is oversimplified. It might be used to describe the physical performances of spatial complicated and multi-dimensions braided composites and rebound to mechanical analysis for the composites.