Abstract: As a new type of aerial digital camera,the airborne three-line array sensor ADS40 now has been more and more popular in the acquisition of high-quality aerial imageries.The object-space back project calculation referring to image point coordinates calculation of the ground points plays a fundamental part in the processing of photogrammetry data.However,the best scanline search is the foremost issue for the object-space back project coordinates calculation algorithm of ADS40 imageries and has becomes the efficiency bottleneck of the current algorithms.We presented a novel object-space back project algorithm for ADS40 images based on central perspective plane of scanline.Experiments proved the feasibility and efficiency of the algorithm,which has currently been applied in the processing module of ADS40 imageries.