After femtosecond laser exciting the metals, photons excite electrons into higher energy levels, and then the excited electrons thermalize rapidly. The higher-temperature electrons transmit energy to the lattice through the electron-phonon scattering process, the electron-phonon coupling factor is used to govern the rate of electron-phonon thermal relaxation process. So far, the size effects of the electron-phonon coupling factor are still in controversial. We explore the femtosecond laser pump and probe method to study the nonequilibrium heat transfer in Au nano metal films, and explore the parabolic two-step radiation heating model to fit the experimental data. By studying on the different thicknesses of Au films′ electron-phonon coupling factors, we find that with the thin film thickness increases, the electron-phonon coupling factor decreases. The experimental data is in agreement with the theory model, which is based on the mean free path forwarded.