Distorted wavefront of the free-vortex aerodynamic windows (FADW) is measured using the method of the lateral shearing interferometry (LSI). And the optical quality factor, i. e., STREHL ratio, is calculated from the reconstructed wavefront. This paper measures the optical quality degradation introduced by the supersonic free-vortex jet of FADW running under the different conditions first. And then it measures the variety of the optical quality with the running time.