In order to meet the requirements of integration of infrared devices and the wideband absorption of infrared light, a novel ultra-broadband, high-absorbance and polarization-independent metamaterial absorber working in the long-wave infrared region (8~14 μm) is designed.By inserting a dielectric layer around the top metal of a metal-dielectric-metal metamaterial absorber to form a metasurface, the resonance intensity and absorption bandwidth can be improved.The structure has an average absorptivity greater than 90% in the range of 8.0 μm to 13.6 μm, covering most of the long-wave infrared atmospheric window bands, which is of great significance to infrared devices. The results indicate that the excitation of Propagating Surface Plasmon (PSP) modes and embedded cavity modes generated by the combination of dielectric-loaded surface plasmon polaritons waveguide and cavity modes contribute to broadband absorption.Moreover, the resonant wavelength of the resonance mode can be tuned by relevant parameters.The results of this paper provide a reference for the design of tunable broadband long-wavelength infrared(LWIR) absorbers. It is suggested that this design method can be extended to the medium wavelength infrared band, the very long-wavelength infrared band and others.