During recent years with improving and extension of technology and using fossil fuels as the main energy resource have resulted in more polluted atmosphere. Problems caused by these pollutants made human beings to conduct research on reduction or elimination of these pollutants. In this regard, research of scientist has let to invention of different types of filters with variety of applications. Among all types of filters, Fibrous filters due to their low price, availability of raw materials, easy production and high efficiency have attracted more attentions. In recent decades advent of Nanotechnology and its entry into non-woven textiles has led to production of Nanofibrous filters. These filters because of their fine diameter, large specific area, acceptable mechanical properties, high flexibility an low basis weight have more efficiency and quality in comparison to other types of fibrous filters. this days These unique characteristics have made this kind of filters as a promising option for reducing particulate matters in the air an improving air quality. Considering the importance and applications of these filters, in this research we are examining different parameters affecting efficiency and quality. For this aim we produced 16 PAN Nanofibrous web with 310 nm mean fiber diameter and four different basis weights on the polyurethane substrate. Electrospinning conditions were chosen according to previous research. In order to evaluate efficiency of filters the filter testing device equipped with particle counter and particle generator has been used. This device we examined effects of different parameters like pressure drop, face velocity and basis weight of Nanofibrous web on the performance Nanofibrous filters. surface morphology of Nanofibrous web in the process of filtration was studied by scanning electron microscopy. In order to investigate influence of Nano fiber diameter on pressure drop and efficiency of Nanofibrou filters we used FLUENT software and Gambit as its pre-processor . Pressure drop and filtration efficiency are two main features to determine quality of filters. Filters having high filtration efficiency and low pressure drop are more desirable. Results of our test showed that pressure drop across the filter will increase linearly with the increase of face velocity. By increasing the face velocity the retention time of particles in Nanofibrous filter will be reduced, thus lower chance for particle to collide on fibers so the lower filtration efficiency would be the result. With the increase in Nanofibrous filter’s basis weight, packing density will be increased, therefor , the collision chance between particles with the fibers will raise. Quality Factor is a reliable indicators to measure performance of filters decreases with the increase of basis weight of Nanofibrous web and face velocity of air due to noticeable reduction in pressure drop. By reducing size of Nano fibers non slip flow regime around the fiber is no longer valid and , effects of slip flow around the fiber surface should be taken into account. Because of the slip occurs around fiber surface particle could be more close to the surface of fiber and subsequently the collision chance will increase; thus, the filtration efficiency will increase too . Keywords : Electrospinning, Nanofibous filters, Filtration, Aerosol, Fluent