Filtration medium is one of the most important parts of air-filtration. A Micro-filtration membrane made by expanded poly-tetra-fluoric-ethylene (ePTFE) was introduced in the dust removal process in our previous work. Compared with conventional fabric media, ePTFE membrane has many advantages, such as low residual pressure drop and high efficiency of dust removal, etc., because of its characteristics of micro-porous structure and slippery surface. More importantly, the useful life of ePTFE membrane is longer and the operating costs are lower during the surface-filtration process. In this paper, the residual pressure drop of the ePTFE micro-filtration membrane and conventional needle-felts fabric filtration medium were compared. The results clearly show that the residual pressure drop of the conventional filter medium increases after several filtration cycles, but that of the ePTFE membrane remains constant.