Abstract: In order to study the hypersonic flutter behavior of rudder models, a hypersonic wind tunnel flutter test technique by continuously varying dynamic pressure was developed and experimentally studied in China Academy of Aerospace Aerodynamics. The models with the same structural and aerodynamic design were tested at Mach number 4.95 and 5.95. The flutter critical parameters were obtained by slowly increasing the dynamic pressure until flutter onset. The short-time-fourier-transform time-frequency domain analysis method was used to study the frequency coupling characteristics. The analysis shows that it is the classic flutter that the bending and torsion mode couples as the dynamic pressure increases. Based on the structural dynamic parameter identification method, the damping ratio extrapolation method and the flutter margin method were used to predict the flutter critical parameters with the subcritical data. Both methods show a good prediction accuracy. The results also indicate that the rate of increase of dynamic pressure has small effect on the prediction of the flutter boundary. The temperature field measurements show that the maximum temperature of the model appears at the leading edge of the wing root. The temperatures of the leading edge and the rear part of the slope of the rudder are also relatively high. The temperature of the leading edge of the rudder shaft exposed to the flow field is not high, which might be due to the influence of the reflector surface boundary layer.