Abstract: Airborne UWB SAR which works in low frequency has large integration angle and long aperture, so the real-time imaging suffers from large amount of data and heavy computational load. Besides, the influence of the motion errors becomes complex and severe due to the long aperture time. All these increase the difficulties of real-time image formation and motion compensation. In this paper, the sub-aperture NCS algorithm is discussed and the modifications in order to reduce the data volume and improve the imaging precision are analyzed. Then the real-time motion compensation strategy based on motion sensor measurements is present. By means of real-time PRI adjustment the variation of the forward velocity is corrected and the across-track motion error will be compensated in the real-time imaging flow. According to the former analysis, a real-time processing flow for airborne UWB SAR on the basis of sub-aperture NCS algorithm with integrated motion compensation is present. At the end of the paper, the real-time processing result of an airborne UWB SAR during a real flight test is present, which validates that the real-time processing flow can meet the demand of real-time and precision of airborne UWB SAR.