In this paper, we present two different auto-scannable terahertz source systems based on the uni-traveling carrier photodiode (UTC-PD), which are the dual-lasers system and the single-laser system. We built the two systems separately and tested their automatic scanning using UTC-PD in W-band(75-110GHz), which was scanned with a frequency resolution of 1 GHz. In the dual-lasers system, the human-controlled scanning took 40 minutes and the automatic scanning took 10 minutes; in the single-laser system, the human-controlled scanning took 30 minutes and the automatic scanning took 3 minutes.