A terahertz optical comb spectral data acquisition system based on high-speed optical asynchronous sampling (ASOPS) method is described. Two femtosecond pulse lasers with a repetition frequency difference of 50 Hz are used as the pump light and the probe light respectively. LT-InGaAs/InAlAs optical antenna is used to generate and receive terahertz signals, and a RF data acquisition system with adjustable sampling rate and optional sampling mode is used to collect time-domain signals and analyze spectral transformation. The spectral width is 0.06~4 THz and the SNR is greater than 60 dB. At the sampling rate of 301.6 MSa/s and the scanning frequency of 50 Hz, the frequency of absorption lines in the experimentally measured water vapor absorption spectrum is very close to that published in the HITRAN database, with a maximum error of 12 GHz.