Wavelength division multiplexing (WDM) technology has been ubiquitously employed in terahertz (THz) communication systems to boost the transmission capacity. However, exploring large bandwidth in WDM-based THz systems pose challenges for the currently existing signal monitoring techniques using either electronic mixers or opto-electronic devices. In this article, a THz sequential equivalent-time sampling (SETS) system using a photoconductive antenna (PCA) for simultaneously capturing multichannel THz communication signals is proposed. A broadband PCA, illuminated by the ultrashort optical pulses from a mode-locked laser (MLL), enables the optical sampling of THz signals. Based on the SETS technique, multichannel THz signals can be equivalently sampled into the low-frequency domain. In a proof-of-concept experiment, three-channel THz quadrature-phase shift-keying (QPSK) signals (∼62 GHz bandwidth) at 100–170 GHz are simultaneously sampled, monitored, and evaluated with a ∼100 MHz sampling rate, and small waveform distortion (DT) of 2.47%, 2.66%, and 3.1% for in-phase components, and 2.5%, 2.74%, and 3.83% for quadrature components have been achieved for three-channel. The proposed THz SETS system brings a new opportunity for exploring more THz bandwidth for wireless communications, and provides a simple, convenient method for simultaneously monitoring multichannel THz signals with beyond 40 GHz bandwidth.