The single-layer SiO₂ chemical films prepared by sol-gel technology were modified with different amounts of ammonia-hexamethyldisilazane (HMDS) atmosphere at room temperature, and then the anti-pollution porformance of the chemical films for dibutyl phthalate (DBP) contamination were tested under low vacuum condition. In addition, the ultraviolet-visible-near-infrared spectrophotometer UV-Vis-NIR), infrared spectrometer and atomic force microscope were used to analyze the evolution of chemical film characteristics before and after modification. The results show that after DBP contamination, the peak transmittance of the chemical film modified by 15-30 mL ammonia-HMDS is 99.8%, which is increased by 3.5% compared with that of the chemical film before modification. At this time, the chemical films have excellent anti-pollution properties. Although the ammonia-HMDS treatment can significantly enhance the anti-pollution performance of DBP contamination of the chemical film, excessive amount of ammonia-HMDS will lead to the laser damage threshold of the chemical film to decrease from 24.3 J/cm² to 19.3 J/cm². The research is helpful to optimize the process parameters to improve the anti-pollution performance of the chemical film, which has great significance for practical engineering applications.