Abstract: Higher requirement of pulse repetition frequency will be faced when Synthetic Aperture Radar(SAR) has low height, high velocity and large squint angle. Too large squint angle will cause doppler centroid frequency deviate from zero greatly, if we still use traditional imaging algorithm, image will defocus. According to the problem of imaging of low-platform and squint-looking SAR, in order to avoid range and azimuth ambiguity and the interference coming from the transmitted pulses, and get high resolution image, designing method of pulse repetition frequency is studied, as a result, the problem of image defocusing is solved. After STOLT interpolate mapping, raw data is properly processed with ω-k algorithm, and good imaging result is gotten. Simulation results testified that the algorithm can solve the problem of imaging of low height and large squint SAR.