Considering the importance of the human respiratory signal detection and based on the Cole-Cole bio-impedance model, we developed a wearable device for detecting human respiratory signal. The device can be used to analyze the impedance characteristics of human body at different frequencies based on the bio-impedance theory. The device is also based on the method of proportion measurement to design a high signal to noise ratio (SNR) circuit to get human respiratory signal. In order to obtain the waveform of the respiratory signal and the value of the respiration rate, we used the techniques of discrete Fourier transform (DFT) and dynamic difference threshold peak detection. Experiments showed that this system was valid, and we could see that it could accurately detect the waveform of respiration and the detection accuracy rate of respiratory wave peak point detection results was over 98%. So it can meet the needs of the actual breath test.