Electret filter materials have a good supplying foreground with the advantages of high efficiency, low resistance, long working time, high dust holding capacity, saving energy and sterilization. The performances of Polypropylene (nonwoven, by needling) fabrics with different densities which are charged, including clean and washed, are tested under the different wind speed and comparison with other materials is made. It has high efficiency to all particles, especially to fine particles. Because of the low resistance it can cut down the consumption of energy. After being washed filtration efficiency to small particles drops greatly. It also analyses its dust holding capacity....