Abstract: The laser output window is very important to the high power lasers. But when the power is very high the conventional output crystal window can not meet the needs of lasers. And the aerodynamic window can take the place of crystal window. This paper analyzes the current study situations and requirement for aerodynamic windows in the field of high power lasers, and then discusses the differences similarities of the laser beam quality evaluating factors' properties. According as the properties of aerodynamic windows it proposes a method of evaluating the laser beam quality of aerodynamic windows for high power lasers using Strehl ratio, at the same time using the beam factor as accessorial factor. This evaluating method is independent of the types of aerodynamic windows, and has been used in