Abstract: Several metal hole array(MHA) structures of different sizes and shapes in THz were designed. The detection sensitivity of the structures with ultra-thin and low refractive index polyimide films, was explored on a THz time-domain system. MHAs with different structures were fabricated with femtosecond micromachining technology, and the THz reflection spectra were measured by the THz time-domain system. By attaching an ultra-thin polyimide (10 m) film to the MHA, an obvious blue-shift of reflective resonance peak was observed, which indicated a high sensitivity of MHA to low refractive index materials. This characteristic allows us to achieve MHA-based high-sensitive sensor at THz band.