In this paper, the periodic rectangular aperture arrays have been etched on a multi-walled carbon nanotube (MWCNT) film prepared by vacuum filtrating to fabricate a terahertz (THz) metasurface on a polyethylene terephthalate (PET) substrate. The transmission properties and the underlying resonance physical mechanism of the metasurface were investigated in detail. An obvious resonant peak located at 0.48 THz can be observed, the results of the scattering powers for various multipole moments show that the enhanced transmission peak is dominated by the radiation contribution of the electric dipole ultimately. To demonstrate the sensing capability, the fabricated metasurface was used to detect different concentrations of 2,4-dichlorophenoxyacetic acid (2,4 - D) solutions. The experimental results reveal that the transmission amplitude decreases linearly as the concentrations increase, and the amplitude sensitivity can achieve 1.69 × 10−2/ppm. This study demonstrates the MWCNT/PET metasurfaces can be applied for trace analytes sensing and improve the sensitivity and accuracy, while the processing technology can also be extended to the preparation and various applications of CNT-based metasurfaces, which provides a beneficial reference for the extended applications of carbon-based metamaterial devices in the THz band.