A high-resolution real-time subaperture imaing formation for range direction pulse compression airborne strip Synthetic Aperture Radar(SAR) system is presented. It can be used in no dechirp strip SAR system. By pulse compression in range direction and Overlapped Subaperture Algorithm(OSA) in azimuth direction this algorithm can compensate the range-azimuth cross error and the space variant phase error. In this study, first strip SAR geometry is analyzed and the strip SAR model is derived, and then the processing flow of OSA for range pulse compression strip SAR system is described in detail. Computation load, data storage and limitations of patch are analyzed then.The point-target simulations and live data processing results show the proposed approach is feasible and effective.