Abstract: MTI & MTD in radar is often utilized to raise the detection performance for the moving target. The analytical expressionof SNR gain of MTI & MTD is derived in this paper, and the gain is not larger than the gain of the only MTD. It is found that thegain of MTD filters on the pass-band center of MTI is nearly unchanged, and the further the MTD filter leaves the center, the largerthe gain change is. The MTI filter makes the noise level unstable, which degrades the following CFAR detection. The frequency response of MTI filter is used to recover the stability of noise level. The above conclusions are of higher value for the practice.