The signal from photoconductive antenna of the Terahertz Time-domain Spectroscopy technology (THz-TDS)is so small compared with the background noise that need amplification by the lock-in amplifier.According to the basic principle of the lock-in amplifier and the characteristics of the THz-TDS,the programmable lock-in amplifier system for THz-TDS based on the AD630 is put forward,which be able to update the chopping frequency and bandwidth according to different samples or working states.The curve between outputs for the programmable band-pass filter controlled by the analog switches on different chopping frequencies and bandwidth can be got by the experiments.And the system’s weak signal detection ability is got by the simulation experiments.At last,in the case of the time-delay line moving speed to 1500 μm/s and continuous scanning,the SNR of THz signal is about 50 dB.The result shows that the system has the advantages of adjustable chopping frequency and bandwidth,good lock-in effect,small volume and easy to be integrated.