Abstract: For the dramatic accumulation of estimation errors during the procedure of the subaperture phase error combining in the persent techniques of autofocus for the conventional strip-mapping mode synthetic aperture radar (SAR) imagery, this article proposes a novel approach to strip-map SAR autofocus, which combines the techniques of phase gradient autofocus (PGA) and map drift (MD). The proposed method also requires that the complete procedure of PGA be accomplished for each subaperture fist. In order to decreasing the accumulation of estimation errors during the procedure of the subaperture phase error combining, the basic rationale of the presented PGA-MD is to adjust and combine the first difference of the subaperture phase error via MD, which can achieve an accurate estimate of the azimuth shift between the neighboring sub-images. Comparison on the accuracy of this approach against the traditional algorithm is presented. Experimental results indicate that the presented PGA-MD methodology can improve the quality of strip-map SAR image effectively.