Abstract: Compressible large eddy simulation was carried out to study the flow field around a hemispherical/cylindrical structure at Mach number of Ma=0.4. Optical path difference and aero-optical phase were calculated according to density data obtained by the large eddy simulation method, and then the aero-optical effect of the wake was studied. The results show that the time-averaged root-mean-square of optical path difference increases with the angle of projection, and it varies from 0.11 m to 0.28 m when the angle of projection increases from 120to 148. Besides, the root-mean-square of optical path difference changes dramatically over time, and its temporal root-mean-square value reaches 0.04 m when the angle of projection is 148. The wake of the hemispherical/cylindrical structure has great effect on laser propagation, and the time-averaged Strehl ratio is 0.33 for the angle of projection of 148. The time-averaged Strehl ratio decreases with the angle of projection, and it reduces 59% when angle of projection increases from 120to 148. The Strehl ratio also changes dramatically over time, and its temporal root-mean-square value is 0.05.