This paper introduced a circuit system based on USB and is designed for TDS（timedomain spectroscopy system）. We can realize the measurement of time domain spectra of samples by controlling the optical delay line using this circuit system to provide bias control for terahertz transmitter, and acquire the data of terahertz detectors which then will be transformed by USB to the PC and finallywe will get the signal time domain and frequency domain signal THz through data processing.By comparison of spectrum pattern recognition algorithm and sample library, identification of objects to be measured component. The terahertz timedomain spectroscopy system can achieve the bandwidth of 3 THz, the spectral resolution is better than 10 GHz, and it can well satisfy the spectral measurement of the samples.