We propose a wide-angle metamaterial absorber with more than 90% absorption in the far-infrared (F-IR) and terahertz (THz) regimes. Our metal-dielectric metamaterial absorber consists of a phase change layer (Ge2Sb2Te5), a dielectric spacer (MgF2), and a bottom refractory metal layer (TiN). We numerically designed the structure by finite-difference time-domain simulation method and demonstrated a perfect absorption in the spectral range from 10 μm to 50 μm (30 THz to 6 THz). Furthermore, it shows a broad peak with maximum absorption of 93% at the resonant wavelength of 22.5 μm when the phase change layer is in the amorphous (disorder) state. In contrast, the peak resonance is red-shifted to 29.5 μm when the Ge2Sb2Te5 switches to the crystalline (order) state, demonstrating a resonant band tunability of Δλ= 7μm. The proposed structure shown here is a simple planner structure, lithographic-free and easy to fabricate with spectral band tunability, which offers great potential for ultra-cooled detection, imaging, security scanning, gas leakage detection, and remote monitoring applications.