Abstract: The impacts of Keystone formatting on SATP are first analyzed. Conclusions are obtained from the study that Keystone formatting degrades the performance of STAP by broadening the clutter ridge and increasing the number of clutter degree of freedom. Based on the above reasons, a novel STAP method is proposed for the detection of fast air moving dim targets when the clutter has no range walk, which removes the clutter firstly, then Keystone formatting is applied for the targets range walk compensation, finally, target is accumulated by conventional space-time beamforming. Hence, the effects of Keystone formatting on the clutter distributions and further on the performance of STAP are avoided. Therefore the good detection performance of fast air moving dim target can be achieved. Effectiveness of the new method is verified via simulation examples.