The HyTRV lift body is a standard model designed for studying boundary layer transition issues in three-dimensional complex geometry at hypersonic flow， with characteristics similar to those of a real aircraft. Currently， research on this model mainly relies on theoretical analysis and numerical calculations， lacking experimental data for validation. To provide wind tunnel test data for theoretical verification and control of boundary layer transition on the HyTRV lift body， we used high-frequency pressure sensors and high-speed infrared cameras to conduct experimental measurements of boundary layer stability in the Mach number 6 Ludwieg tube wind tunnel. The study analyzed the instability characteristics of the boundary layer in the flow separation region， the transverse flow region， the waist transverse flow region， and the shoulder flow separation region of the HyTRV model， with a focus on investigating instability waves in the transverse flow region of the model belly. The experimental results show that the vortex region of the HyTRV model belly exhibits weak low-frequency instability waves at 10-30 kHz， while high-frequency instability waves of 150-250 kHz were measured in the cross-flow region of the belly. At a 0° angle of attack， the propagation speed of this instability wave was determined to be 722.9 m/s， suggesting that this instability wave is a high-frequency unstable mode of the secondary crossflow instability. The process of boundary layer transition was observed in the waist crossflow region and the shoulder vortex region， with no obvious instability wave characteristics found. Infrared measurement results show good agreement between the model leading edge and trailing edge transition fronts and direct numerical simulation results. Additionally， typical sawtooth-like streaky transition arrays were observed on the model leading edge， consistent with the conclusion that cross-flow instability dominates unstable transition in the cross-flow region of the belly.