Abstract: The interferometric Rayleigh scattering diagnostic technique for the time-resolved velocity measurement of the transonic wind tunnel is studied. The velocity-measurement apparatus, consisted of a CW laser, a high resolution Fabry-Pérot interferometer and a high-speed EMCCD camera, is designed. Rayleigh scattering light is produced as the flow irradiated by the laser. Then the light is collected and analyzed accurately by the Fabry-Pérot interferometer and the camera. Theoretically, this systematic velocity-measurement accuracy can reach 1.23m/s. Measurement accuracy is then evaluated by comparing with hot wire anemometry results. Moreover, the distributions of velocity and turbulence intensity in a supersonic flow at Mach number 3.0 are obtained quantitatively. The sampling rate in this measurement reached about 4 kHz.