Aiming at the requirements of localization, high performance and flexibility and portability of terahertz time-domain spectrometers, the principle of sequential equivalent sampling of weak terahertz pulse signals is analyzed, and a high-speed direct data acquisition system for terahertz photoconductive detection is designed. A direct-acquisition terahertz time-domain spectroscopy fast scanning system composed of femtosecond pulsed lasers, motorized optical delay lines, terahertz photoconductive antennas, direct data acquisition systems, three-axis displacement platforms, semiconductor refrigeration thermostats and PC computers. Finally, the system is tested and analyzed. The experimental results show that, under the same no-load test conditions, the system has a 9dB increase in the frequency domain dynamic range of the signal compared to the traditional SR830 lock-in amplifier system, and a 0.4THz increase in the effective spectrum width. After 512 times of time domain averaging, the system signal spectrum is the dynamic range exceeds 72dB and the effective spectral width is up to 3.5THz.