Target acceleration of SAR moving target detection results in three-phase, and affects stationary target suppression and the precision of parameter estimation. Aiming at this problem, a parameter estimation method based on three-phase compensation is proposed. According to the analysis of signal model, phase compensation is achieved by dechirp and one-dimensional search in time-chirp distribution. After the phase compensation, in order to overcome potential problem of target loss caused by peak overlap in time-frequency distribution, an improved FrFT is employed for parameter estimation and the method is given in detail. Finally, the computer simulation confirms the correctness and validity of the method.