Abstract: Estimations of the first two order power spectrum moments from autoregressive approach (PPARNC) and covariance approach (PPCNC) with independent pulse pair by noise cancel method and from autoregressive approach (PPARML) and covariance approach (PPCML) with independent pulse pair by maximum likelihood method are analyzed with the assumption that the input signal and noise are independent colour complex Gaussian process.It is shown that PPARNC and PPCNC are better than PPARML and PPCNL,and PPARNC is the best of air.