Abstract: 5 typical needle felts were treated by multiple needle corona discharge to study the optimal electret filter， charge parameters and the performances of electret filter such as particle capture efficiency and charge stability. The results showed that the efficiency of all types of filters were improved in different extent: the increase of filtration efficiency of the polytetrafluoroethylene(PTFE)membrane filter is the largest with the smallest attenuation. The charge reservation percentage after a month of the PTFE filter treated under the condition of 15kV of charging voltage， 2cm of electrode distance and 20min of charge time is 62.22% with less than 0.9% of filter efficiency reduction for particles smaller than 1μm. After heat treatment of 200℃， the average charge reservation percentage of PTFE is 56.15%， and the efficiency reduction for particles smaller than 1μm is less than 1.23%. The charge technology has a prominent enhancement effect for PTFE membrane filter.

Key words: electret filter, corona disc charging, stability, fine particle, filtration efficiency