Abstract: Equivalent radar speed is an important parameter to realize SAR imaging, which can directly affect the focusing effect of SAR image. At present, the equivalent radar speed can be estimated through orbit and attitude data, but the data is difficult to obtain, and the equivalent radar speed can be estimated by using the existing autofocusing technology through SAR echo data, which has problems such as low accuracy and slow speed. In this paper, a SAR equivalent radar speed estimation method based on NELDER-MEAD search algorithm is proposed, which uses image contrast and optimization theory to maximize the contrast of SAR images by searching for a certain speed value and then estimates the equivalent radar speed. The proposed method allows to quickly estimate stable and accurate equivalent radar speeds at loose initial values without specifying the search range, and achieve high-precision SAR imaging. This study provides a reliable solution method and idea for estimating the equivalent radar speed of spaceborne SAR, and this method has application value for studying SAR imaging accuracy at the practical level.