Micro-motion of helicopter blades forms the micro-Doppler effect, which is a kind of important characteristic and is extremely important for identifying different types of helicopters in the battlefield environment. Determining the micro-motion characteristics of helicopter rotor is the precondition for the identification. Because of the short wavelength and significant Doppler effect of terahertz radar, it is urgent to determine the fretting characteristics of the rotor target in terahertz band. Firstly, the propeller targets with even and odd blades are modeled. Then, the targets are simulated by using the radar in microwave band(3 GHz) and terahertz band(120 GHz, 220 GHz), and the Doppler frequency shift information is extracted from the characteristics of the target echo signal. Using Short Time Fourier Transform(STFT) in time-frequency analysis, the influence of the target and the radar parameters on the Doppler effect and the modulation relationship are contrasted. The simulation results show that the micro-Doppler effect in Terahertz band is more significantly enhanced than that in microwave band, and the Doppler curve is clearer and more details of the blades can be observed under the condition of the same rotation speed, angle of view and blade length. Using terahertz radar to extract micro-Doppler information can provide significant features for helicopter target recognition.