Fluorination modification and electret properties were studied on the cellular polypropylene (PP) films modified by gaseous fluorine by attenuated total reflection (ATR) infrared analysis and the measurment of open-circuit thermally stimulated discharge (TSD) current，in situ TSD charge and isothermal charge decay. The results showed that the PP cellular films，especially the preoxidized ones，can be effectively fluorinated by gaseous fluorine，and that charge storage thermal stability of the fluorinated films，especially the fluorinated preoxidized ones，is significantly improved compared with that of the virginal PP film，even under conditions of negative pressure with a low partial pressure of gaseous fluorine，low reaction temperature about 60℃ and short reaction time of 15min.