Abstract: The velocity and turbulence level of Mach 5, 6 and 12 flow fields have been measured in the Φ0.3m hypersonic low density wind tunnel by the Rayleigh scattering principle using a Fabry-Perot interferometer. The application of the Rayleigh scattering measuring system in the velocity measurement of the hypersonic flow field is understood and realized. The turbulence level of the wind tunnel is below 1%, and the maximum deviation between the velocity measurement result and the flow-field calibration is 1.3%. The velocity in the flow field around the re-entry module after the shock wave has also been measured. The experimental result of the Mach 6 incoming flow is in agreement with numerical simulation results, but in the case of the Mach 12 incoming flow the deviation is 69%, and the reason is analyzed. It is found that through the experiment a certain condensation exists in the Φ0.3m hypersonic low density wind tunnel. Further research scheme is suggested.