A series of experiments with different charge aerosols were carried out to investigate the mechanism of static electricity attenuation for fibrous filter medium. DEHS and three different charge characters of KCl were used to challenge electrostatic fibrous filter medium. The surface potential and filtration efficiency were tested and morphology of medium was observed through scanning electron microscope (SEM) for different dust loading periods. The results of experiments show that surface potential of filter mediums challenged with charge KCl (Potassium chloride) has different variation trends with dust collection, however, the efficiency does not change obviously. Surface potential and efficiency of filter mediums challenged with diethyl hexyl sebacate (DEHS) decrease sharply. Both experimental results and SEM of medium challenged with different morphology show that the mechanism of electrostatic attenuation for filter medium is mainly due to electrostatic shielding effect.