Radio frequency plasma enhance chemical vapor deposition (RF-PECVD) was used todeposit nitrogen doped fluorinated amorphous carbon (a -C:F,N) films with CF4, CH4 and N2 as source gases. We focused on the influence of annealing temperature on the structure and optical band gap (Eg) of the films. The as-deposited films undergo significant chemical and optical changes during annealing. The films are thermally stable at 350℃. The optical band gap shows decrease of different degrees with increasing annealing temperature. Raman and Fourier transform infrared absorption spectra show that the relative content of F in the films decreased, while the content of sp2 carbon increased, and as a result, the density of states near the band edgye of σ-σ* decreases, which is responsible for the increasing Eg.