Nitrogen doping fluorinated amorphous carbon (α-C: F) films were deposited using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) and annealed in Ar environment in order to investigate their thermal stability. Surface morphology and the thickness of the films before and after annealing were characterized by AFM and ellipsometer. Raman spectra and FTIR were used to analyze the chemical structure of the films. The results show that the surface of the films becomes more homogeneous either by the addition of N2 or after annealing. Deposition rate of the films increases a little at first and then decreases sharply with the increase of N2 source gas flux. It is also found that the fraction of aromatic rings structure increases and the thermal stability of the films is strengthened with the increase of N2 flux. Nitrogen doping is a feasible approach to improve the thermal stability of α-C: F films.