Under the condition of platform maneuvers, the accuracy of the motion compensation in frequency-domain cannot meet the focusing need of airborne Ultra-wideband Synthetic Aperture Radar (UWB SAR) because of strong motion errors. The time-domain Back Projection (BP) algorithm can be used in this instance, whereas the large amount of computation limits its application. In light of this, a strategy of processing the airborne UWB SAR data with platform maneuvers is proposed by using the Sub-image Fast Factorized Back Projection (SIFFBP) algorithm. The constrain relationship between the sub-aperture and sub-image factorization was derived, and then the implementation approach was listed with the computation volume being analyzed. The processing results of the simulated and real data show that SIFFBP algorithm is applicable for the focusing of airborne UWB SAR under the condition of platform maneuvers with high precision and efficiency. 