Abstract: To the damage caused by surface contaminants from the reflector in the high power solid laser facility, the offline experiment and online experiment were carried out respectively, the remove rate of surface contaminants was investigated based on air knife combining dark field imaging technique. Experimental results show that when the deflection angle of the air knife is 0° and the distance between the air knife and the surface of large-aperture reflector is 10 mm, the removal effect of dust particles is the best, up to 96.5%, followed by particles of Al₂O₃ and Fe with same size, particles of SiO₂ with same size is weakest, and the online average removal rate can reach 84.9%. Through the online research on the deposition law of particles pollutants on the surface of the large-aperture reflector, it is shown that the long-term cleanliness of the reflector surface can be realized by using the air knife sweeping technology once a week, which can be extended to large-aperture high-energy laser facility and future super large-scale high power laser facility.