Doppler frequency rate is one of the key parameters in the azimuth processing of SAR data. Once mismatched, it will cause serious defocusing in azimuth dimension and then result in the degradations of image quality. On the other hand, fast estimation for Doppler frequency rate is necessary for the sake of disaster mitigation. To meet the need of fast estimation of Doppler frequency rate, an approach based on geometry and SAR echo data is put forward in this article, which can simplify the estimation processing according to the relationship between the Doppler frequency rate and range. Besides, the selection strategy for block data used to estimate the Doppler frequency rate is discussed. In the end, corresponding results have been given.