A theoretical model has been developed to evaluate the effect of geometrical parameters of three-dimensional fabrics on hydraulic radius of different fabric structures. Results show that the hydraulic radius increases logarithmically with the increase of weave spacing between yarns and is independent on the yarn diameter. As any fabric is composed of a certain percentage of one to four different pore types, its hydraulic radius can be evaluated by taking the composition of pore h,pes and hydraulic radius of pore types into account. The analytical result of the model can be used to design and select woven fabrics in accordance with the filtration requirement, encouraging textile industry to develop new fabrics to meet the requirement of specific industrial applications.