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A multi-band absorber based on a hybrid metal-graphene metasurface, which is also suitable for detecting surrounding refractive index, is proposed and studied by numerical simulation. The structure combines a metal disc with a graphene plasmon, which greatly enhances the coupling of light and graphene, and realizes multi-band resonance absorption. The simulated results show that three absorption peaks at 23.5 µm, 24.3 µm and 27.8 µm with the maximal absorption of 96.4%, 99.4% and 99.9% have been achieved, respectively. At the same time, under normal incidence, the absorber is not restricted by the polarization angle of the incident light source. Moreover, the light source can be incident obliquely under two polarization conditions, and the absorber of this structure maintains approximately stable absorption within the range of oblique incident 50°. The dynamic adjustment of the absorption peak can be achieved by flexibly changing the Fermi level of graphene. Furthermore, the absorber we proposed can also be used as a refractive index sensor to detect the surrounding refractive index. The sensitivities are 3.98 µm/RIU, 4.13 µm/RIU and 5.06 µm/RIU, and the maximum figure of merit (FOM) is 16.6, 20.7 and 18.1, respectively.