We present a simple quad-band terahertz (THz) metamaterial absorber for perfect absorption. Unlike most reported absorbers, the proposed structure achieves perfect absorption based on high-order plasmon resonance, with the absorptivity of the first three peaks all >99.4  %  . First, the resonance absorption mechanism of the absorber involving fundamental resonance mode and high-order resonance mode is analyzed in detail. Next, the sensing performance is also studied by changing the ambient refractive index, the numerical results show that the designed multiband metamaterial absorber is very sensitive to small changes in refractive index, and appears highly sensitive in its sensing performance. In particular, figure of merit of the last absorption peak reaches 26.6, which is far superior to most multiband metamaterial absorbers operating in the THz regime. The proposed simple structure not only greatly simplifies the fabrication, but also is insensitive to the polarization of incident waves. The results show that the quad-band metamaterial absorber has potential applications in sensing, imaging, detection, and other fields.