The instability characteristics of swirling flow in the cyclone were studied based on measured real tangential velocity by hot wire anemometry（HWA）.The results showed that the real tangential velocity fluctuated obviously in the center region of the cyclone，however，near the wall of the cyclone，the real tangential velocity had a little fluctuation.The real tangential velocity was analyzed with Fast Fourier Transform(FFT).There was a basic frequency near the center region of the cyclone，which was about 44Hz.And the amplitude in the center region was bigger than that near the wall.The real tangential velocity fluctuation indicated that there existed an instability of swirling flow in the cyclone.This instability resulted in the rotation center of the swirling flow deviating from the geometric center of the cyclone，which produced the quasi-periodic oscillation of swirling flow and gave the real tangential velocity fluctuation.