Inverse synthetic aperture radar (ISAR) is an important approach to derive d etailed information of wideband radar target, where defocusing caused by complex motion and low resolution are two key difficulties. This paper gives a survey o f radar imaging of complex motion target, including modulation effect of micro m otion, procession target imaging, three dimensional motion target imaging and s e parate motion parts imaging. Aiming at improving image resolution, coherent comp ensation among sub bands and fusion imaging are also demonstrated. Then new app r oaches of radar imaging are presented, wherein radar coincidence imaging is irre levant to the relative motion between radar and target, thus avoid compensating complex motions. In THz imaging it is easy to implement large bandwidth and narr ow wave beam; thereby the formulated high resolution images are with more detail s which are beneficial to target recognition. Finally, difficulties and directio ns for these two newly developing techniques are pointed out.