By using the unsteady computation which employed phase-lag method to get the fluctuation pressure in a high pressure turbine stage with real blade amount

and also using the mode matching method in the duct of downstream rotor

the non-physic reflection in the duct end and other non-sound pressure fluctuations were extracted.The rotor-stator interaction noise propagating downstream was obtained.The results show that the dominance azimuthal mode m=3 isn't cut-off for the blade passing frequency

m=6 and m=-64 aren't cut-off for the second blade passing frequency.