Objective To study the influence of the background pressure and the residual gas in the coating crate on optical properties of the laser film so as to improve the laser resistance of thin film when using the vacuum coating machine for coating. Methods A vacuum coating equipment was borrowed for the experiment. For the convenience to conduct qualitative and quantitative study, different background pressures were preset specifically in coordination with different residual gases and other conditions to prepare the laser film. Each kind of laser film was tested to investigate the specific influence of different setting conditions on preparation of laser film. Results Experimental results showed that the anti-laser damage threshold of the film was the highest when the oil and gas was at a partial pressure of 1. 6×10-3 Pa. The greater the partial pressure of water vapor was, the smaller the anti-laser damage threshold of the laser film would be. When the oxygen partial pressure reached 1. 5×10-2 Pa, the anti-laser damage threshold began to decrease dramatically. When the pressure was less than 2. 0×10-4 Pa, the anti-laser damage threshold of the film increased with the increase of the background pressure. When the pressure was greater than 5. 0×10-5 Pa, the anti-laser damage threshold of the film gradually decreased. Conclusion Increasing the background pressure of the vacuum equipment and reducing the amount, composition and content of residual gas in the vacuum system, especially H2 O and O2 , is the key to improve the optical performance of laser film.