Abstract: By the laser beam deflection effect in air density gradient field,the laser deflection diagnosis system was designed,and the air density change dused by the aeronautical plasma actuators was diagnosed.The results showed that the air density decreased by -1.7% in the vicinity of the upper electrode’s edge between two electrodes,and increased by 0.27% in the vicinity of the lower electrode’s edge between two electrodes.The measurement results were consistent with the results of other means.But the diagnosis of the laser deflection system is faster and more effective.

Key words: laser deflection system；air density, harassment, index of refraction