To improve thermal stability of Teflon FEP which is the most widely used materials for electret application, Teflon AF film of 1 $mu extrm{m}$ thick was spin coated on FEP film and the charge storage properties were investigated. The surface potential depend on aging temperature. Thermal Stimulated Current(TSC), Atomic Force Microscopy(AFM), and Fourier Transform-Infrared Spectroscope(FT-lR) measurements were carried out. It is shown that the AF/FEP dual film have more higher electrical property and thermal stability than that FEP film have caused by charge stored at interface of AF and FEP.