In this paper, the SBR-VRT hybrid method is used to calculate the radar echoes of targets located above rough ground surface covered by vegetation. The maximum likelihood (ML) method is used to estimate the parameters of the clutter amplitude probability density function (PDF), and the K-S test is used to evaluate the goodness of fit between the clutter PDF and the different models PDF, and determine the best distribution fitting results. The features of ground clutter wave amplitude distribution under different conditions, including frequencies and angle of incidence, are studied, and the best distribution fitting results under different conditions are given. It can be found that the PDF of clutter amplitude at large incident angles under the L-band and S-band, is Log-normal distribution.