Long-time coherent accumulation is an effective method for radar detection of small targets in low altitude. However, for targets with high speed, long-time coherent accumulation has the problem of range walking. To solve this problem, a detection method of low altitude small target based on keystone transform is proposed in this paper. First , the problem of long-time coherent accumulation in low altitude small target detection is presented. Second, the detection method based on keystone transform and its fast implementation method are proposed. Finally, the simulation results of a typical target is given. The proposed method can simultaneously solve the problem of unified detection in a large speed range, and the simulation results verify the effectiveness of the proposed method.