In vacuum and space environment, laser damage resistance of the optical film reduces greatly. This is mainly due to the coupling effect of organic pollution in the vacuum environment and the internal defect of the film, which results in the enhancement of the light field of film. The protective film technology is an effective measure to improve the ability of optical film to resist laser damage. Based on the finite-difference time-domain algorithm, the inhibition effect of the protective layer on the light field enhancement induced by the coupling of organic pollution droplet and defect was analyzed. The analysis result shows that the light field peak value of TiO₂ film decreases with the increase of protective layer thickness. When the refractive index of the protective layer is the middle value of the organic pollution droplet refractive index and that of the film , the inhibition effect of light field enhancement is the greatest. The experimental results have verified the theoretical analysis. This study deepens the understanding of the mechanism of laser induced damage degradation of optical film in vacuum and has certain reference value for improving the laser damage resistance of optical film in vacuum environment.