Most synthetic aperture radar (SAR) applies to static targets while moving targets appear unfocused in SAR images. To obtain clear images of moving targets, the Doppler parameter estimation is critical in SAR processing. However, most of the time–frequency analysis methods cannot simultaneously meet the requirements of accuracy and real time. A real-time parameter estimation algorithm based on Wigner–Ville distribution (WVD) slice and fractional Fourier transform (FrFT) is proposed. In this algorithm, the Doppler frequency rate is roughly estimated through the observed signal's WVD slices first. Then, its corresponding FrFT rotational angle is deduced and the search region is determined. Next, Doppler parameters can be accurately estimated by FrFT under the premise of reducing the computational complexity. Three reasonable choices of the slice positions are given and their estimation results are explained. SAR real data processing results indicate that the proposed algorithm can estimate Doppler parameters quickly and effectively while ensuring accuracy and providing a new way for SAR real-time parameter estimation. Finally, motion compensation in accord with the estimated parameters is also completed and focused images of several moving ship targets are obtained.