Abstract: For the effect evaluation problem of the multi-false-target jamming against constant false-alarm rate（CFAR） detection radar, the detection threshold of CFAR detection in multi-false-target jamming was studied according to the principle of the CFAR detection, and the jamming effect of the multiple false targets with different interval was analyzed. The conclusion is that the radar with CFAR detection method will output no signal by the effect of the multi-false-target jamming with stated power and density in the specific false alarm probability. At last the simulation was done to prove the analysis. The research can be used to design the multi-false-target jamming.