Super-broadband spectrum detection technology has an important significance for high-resolution terahertz (THz) absorption spectrum measurements, as well as scientific research and application of terahertz development. We use air plasma as the detection medium and successfully detect super-broadband THz spectra. The detection mechanism is investigated by experiments. We use the system to measure two kinds of explosives′ super-broadband absorption spectra. The results indicate that THz spectra widths increase with pump power or bias, and super-broadband absorption spectra match well with Fourier transform infrared (FTIR) pectra in low frequency area.