With the size reduction and operation frequency increase in electronic devices and high radio frequency radar，and wide application of femotosecond laser ablation，electron-phonon coupling in metals plays a more and more important role.However，it is still an open question whether the electron-phonon coupling in polycrystalline thin metallic films will be affected by size effect.In this paper，the electron-phonon coupling in several gold films of different thickness has been studied by using rear-pump front-probe thermoreflectance technique.The measured electron-phonon coupling factors are nearly the same as that of bulk gold and independent of film thickness.It has been found that the electron energy relaxation in thin gold films occur through bulk electron-phonon，electron-grain boundary，and electron-surface couplings.But the strength of electron-grain boundary and electron-surface coupling is sufficiently weak compared to the corresponding bulk electron-phonon interaction.