In order to improve the environmental adaptability of airborne infrared optical systems, the effects of ambiance temperature upon an IR optical system was analyzed, and several typical athermal compensation methods were compared.The optical layout and athermal compensation of the optical system were studied.Firstly, the active athermal compensation method was proposed based on the nonlinear speciality of the lens athermal compensation.Then, it pointed out that the normal cam-potentiometer method could not meet the demands, so the stepper motor with 0.006 mm was selected as a driver.Aim at the disadvantage of proposed method, a linear Hall sensor was introduced to be a position feedback component,and precision athermal compensation was realized by a partial fit method.Finally, the zoom and athermal compensation mechanical structures were discussed.Experimental results indicate that the method proposed can get 0.02 mm compensation precision, and the MTF attenuation of IR optical system is within 0.05,which satisfies the system requirement of athermal compensation in the full temperature range.