A stack of polymide （Kapton/PI） films was irradiated with 22.5MeV/u high energy Ar-ions. The conductivity measurement and the ultraviolet-visible absorption spectra of the modified Kapton show that the conductivity and the absorbance increased and the absorption edge is gradually shifted from near UV to visible with the increasing of electronic energy loss in unit volume. It can be concluded that electronic energy loss plays a key role in polymer modification.