In this paper, we first introduce our newly devised ISAR autofocus algrithm AUTO-CLEAN. Then the feature extraction step is further studied, and investigation results show that CLEAN isa good candidate. AUTOCLEAN is not only a robust ISAR autofocus tool. but also can be used for the au-tofocus of spotlight SAR, curvilinear SAR, and interferometric SAR with two antennas.