We measured the terahertz time-domain electric fields of alumina and aluminum hydroxide samples in the range of 0.5-1.5 THz using terahertz time-domain spectroscopy. The frequency-domain spectra of sample and reference signals containing the amplitude and phase information were obtained by the fast Fourier transform of the measured time-domain signals. Compared with the frequency-domain spectrum of a reference signal, one can find that the aluminum hydroxide sample has obvious characteristic peaks at 1.20 THz and 1.33 THz; however, the alumina samples have the same characteristic peaks as the reference signal. The near-field enhancement via the surface plasmon polaritons of graphene was used to enhance resonant stretching of the hydroxyl groups in a molecule by doping a certain proportion of graphene and aluminum hydroxide, and thereby the enhanced regulation of characteristic peaks of aluminum hydroxide is achieved. This study not only offers effective nondestructive test and identification of aluminum hydroxide, but also increases the detection sensitivity of aluminum hydroxide using graphene. Moreover, it has reference significance for further study of spectral information for other hydroxides using terahertz time-domain spectroscopy.