There is a close relationship between jet shear layer and acoustic refraction, but research on the unsteady characteristics between them is relatively inadequate. Firstly, the relationship between the sound ray direction and the vorticity, which is the classical ray tracing method, was simply derived, and the applicable conditions were focused on to extend it to the unsteady conditions. Then, the concept of effective area of sound refraction was proposed for beamforming sound source identification array. Sound propagation experiment was carried out in a 3/4 open-jet acoustic wind tunnel by using microphone array and controllable sound source with low flow resistance and self-noise, and the unsteady acoustic drift of initial source with different frequencies was measured. After that, the flow structure of same wind tunnel, especially the jet shear layer, was simulated and verified, which proved that the shear layer formed by the straight section of one nozzle side is quasi two-dimensional. In the simulation, 30 monitoring areas were divided along the shear layer, and the variation of vorticity integral value in each area was analyzed. Finally, similar to the Amiet method, the volume of the effective region was ignored, and several conditions that could be satisfied in this paper were introduced to establish a linear relationship between regional vorticity and acoustic drift. Through the comparison between the acoustic drift of direct measurement and vorticity calculation, the validity of the linear relationship at the time average and instantaneous levels is proved. The research of this paper show that the relationship between vorticity and acoustic ray is still valid at unsteady level as long as the conditions of low-speed flow and high frequency sound are satisfied. At the same time, it provided a new idea for non-contact flow measurement in shear layer of jet structure.