Abstract: A series of experiments were conducted in a high speed wind tunnel to study aero-acoustic characteristics cavity flows. The rear wall of the tested cavity was chamfered to reduce the airflow impact strengthen, so as to suppress the cavity noise. The test Mach numbers ranged from 0.6 to 1.2. The length to depth ratios of the cavities were 4.1 and 4.7. Results indicate that aero-acoustic environment around the open cavity exacerbates with increasing Mach number in subsonic and transonic speed ranges. The maximal overall sound pressure level (OSPL) is more than 170dB. Several tones with different modes can be found in the sound pressure spectra. It is also indicated that the control method by chamfering the cavity rear wall is effective on suppressing the cavity noise. The overall sound pressure level on the cavity floor reduced significantly, the maximum of reduced OSPL was approximately 7dB. The reduced OSPL was about 1dB near the main noise source on the rear wall of the cavity. The peaks of sound energy spectrum curves were also suppressed substantially due to the control method.