Abstract: In order to study HF channel Doppler power spectral density（PSD)， the ionospheric movements were assumed to be two different motions of the regular layers and the irregularities， based on which an expression of Doppler shift was deduced.Then the probability density function（PDF)of Doppler shift was derived，which left electron density variance with time and the effect of the variance of geomagnetic field with time out of account.On condition that the receiving antenna is omnidirection， the PSD function of the scattering signal component was obtained，which shows the PSD is of a mixture Gaussian shape.The mixture Gaussian shape curve fitting of Doppler PSDs of the data acquired in experiment were made by looking out the minimum standard deviation of error sequence and the fitting results indicate the validity of the theoretical deduction.