Abstract: Cross flow instability is one of the dominant modes of hypersonic boundary layer transition in real flight. However, the mechanism of hypersonic boundary layer transition induced by cross flow instability is still out of understanding. In this work we carried out the hypersonic instability experiment on a 6 degree hypersonic sharp cone model with rough surface using high-frequency pressure sensors, infrared camera, and hot-wire anemometry. The evolution of instability waves along the streamwise direction was obtained for different circumferential angles, and the development of low-frequency instability waves across the hypersonic boundary layer was also characterized. The results denote that the low-frequency instability waves are travelling cross-flow instability, while the high-frequency instability waves are speculated to be the secondary instability induced by the stationary cross-flow instability.