Metamaterial absorbers in terahertz band can be widely used in military radar and biological detection. In this paper, a terahertz metamaterial absorber with a T-shape structure is proposed. Its absorptivity can reach 99.99%, close to perfect absorption. The factors influencing absorptivity and the absorptivity mechanism of the structure are disclosed from the aspects of structural size and current distribution. In order to make the above T-shaped structure apply to a wider range, the designs of a polarization- insensitive T-shaped absorber and a frequency- adjustable T-shaped structure absorber are further proposed. The simulation shows that the designed metamaterial absorber has high absorptivity, flexible frequency adjustment range, and insensitive polarization angle, so it has good research value.