In order to study air pressure influence on imaging quality of vehicle-mounted photoelectric system,a mathematical model of air pressure leading to image blurring of photoelectric system was established based on the analysis to the influence of air pressure variation on defocusing of photoelectric system.Optical system model of a certain type of wheeled artillery sight was established,the simulation analysis of system model was carried out by setting different ambient air pressure,and simulated images of the sight under different air pressure were obtained finally.Simulated images were evaluated by using gray mean gradient,and the conclusion was summarized: the lower the air pressure,the more blurred the image,and the worse the imaging quality of the sight.The study is of great reference value to environmental adaptability design of new type vehicle-mounted photoelectric system.