The influence of N2 plasma annealing on the properties of fluorine doped silicon oxide (SiOF) films is investigated.The stability of the dielectric constant of SiOF film is remarkably improved by the N2 plasma annealing. After enduring a moisture absorption test for six hours in a chamber with 60% humidity at 50℃, the dielectric constant variation of the annealed SiOF films is only 1.5%, while the variation for those SiOF films without annealing is 15.5%. Fourier transform infrared spectroscopic results show that the absorption peaks of Si-OH and H-OH of SiOF films are reduced after the N2 plasma annealing because the annealing can wipe off some unstable Si-F2 bonds in SiOF films. These unstable Si-F2 bonds are suitable to react with water, resulting in the degradation of SiOF film properties. Therefore, the N2 plasma annealing meliorates the properties of SiOF films with low dielectric constant.