Terahertz time-domain spectroscopy on-chip system concentrates the generation, transmission and detection of terahertz on a few millimeters of substrate, and relies mainly on the surface plasma effect to realize the interaction between terahertz waves and trace samples in the detection region of the samples. Compared with the traditional THz-TDS system, the terahertz time-domain spectroscopy on-chip system is characterized by high integration, small system size, and favorable for the detection of trace samples in aqueous solution. In this paper, we mainly design and build a terahertz time-domain spectroscopy on-chip system, and realize the characterization of the performance of terahertz detection chip, and explore and analyze the reason of system noise. Through this system, it is verified that the low resistivity of the LT-GaAs material used on the terahertz detection chip leads to leakage at the emitter, so that the photocurrent generated at the emitter is directly received at the probe end, which then generates the background noise of the system. This work lays the foundation for the subsequent research and development of terahertz time-domain spectroscopy on-chip systems, and provides a theoretical basis for improving the signal-to-noise ratio of terahertz time-domain spectroscopy on-chip systems.