Abstract: In this paper the Doppler spectrum measurement ability of air targets including helicopter and fixed-wing aircraft is analyzed firstly. Then the Doppler spectrum features of these two kinds of targets are analyzed provided the measurement ability is satisfied. Differences petween the spectrums are found and a method for identifying these two kinds of targets is suggested. This method has been proved to be efficient by testing the simulated data of the eighteen kinds of helicopters and fixed-wing aircraft and on-the-spot measured data. This method can also be applied to detection and identification of hovering helicopter.