The simulation of the mean flow over airborne laser fairing as well as its aeroptic analysis with selected area electron diffraction software is presented. The simulation reveals that the aero-optic effect with respect to the mean flow field strongly depends on the beam direction: along different beam propagation directions, the root mean square of optical path difference varies between 0.13~1.20 μm, and tilt angle of beam axis varies between 1~12 μrad. Furthermore, the wave-front distortion caused by mean flow-field aeroptic effect is mainly low-order effect: the ratio of tilt to the aberration is about 92%, and the ratio of tilt, defocussing and astigmatism is about 99%. The average of beam quality factor β over all directions caused by no-tilt wave-front aberration is 1.8; when defocussing and astigmatism is corrected, the average of beam quality factor β is 1.16. The beam quality factor β caused by no-tilt aberration increases with the increment of beam radius as a nearly linear manner.