Material separation involves a wide range of research fields, generally including material properties, material quality, filtration mechanism, separation effect, etc., among which filtration accuracy is the key technical index for filter material assessment in all purification processes. Due to the differences in the material and structure of the filter medium, the determination of filtration accuracy is mostly in accordance with the international standard ASTM F 795(liquid-solid separation method). The testing methods are complex and susceptible to the test conditions. According to the characteristics of the micropore structure of rigid sintered wire mesh, which is formed by high precision loom, a reasonable formula for calculating the pore size is presented in this paper. This formula can be used to calculate the effective aperture of single layer plain mesh and twill mesh effectively, which ensures the relatively reliable filtering accuracy and provides theoretical basis for the development of more accurate screen.