A frequency domain detection method is proposed aiming at the problem of target echo signal detection in indoor personnel localization and tracking system based on frequency module carrier wave（ FMCW） radio wave reflection. Frequency offset between after reflected echo and difference frequency signals of FMCW are sampled M times

and then transfer to frequency domain signal

detection threshold of difference frequency signal in frequency domain is set by constant false alarm rate（ CFAR）

through comparing threshold

the first component of frequency is judged and thus echo signal detection of the target is realized. Relationship between CFAR and frequency dmain threshold is obtained by derivation

and the effects of different parameters on the detection performance are analyzed. Simulation results show that the proposed detection method can accurately extract the first frequency component of echo signal.