Abstract: Polyamide 6 (PA6) nanoscale fibers were prepared from 22% PA6 / formic acid solution by electrospinning. Three kinds of common nonwoven fibrous filters were used as collecting substrates during the electrospinning, so that the PA6 nanoscale fiber layer and the substrate were made into composite mats. The pore structure of the nanoscale fiber composite mats was investigated, and the relationships between the nanoscale fiber solidity, substrate and porous characteristic of the PA6 composite mats were analyzed. The air permeation rate, filtration efficiency and filtration resistance of the compsite mats were tested. The results reveal that with the nanoscale fiber solidity increasing, the number of pores in the composite mat increases exponentially, but the average pore area, porosity and air permeation rate exponentially decreases. The air permeation rate shows good linear relation with the porosity. The filtration efficiency of nonwoven fibrous filter is obviously improved due to the nanoscale fiber layers in a composite mat.