We propose a tunable multilayer-graphene-based broadband metamaterial selective absorber using the finite-difference time domain. The simulation results reveal that the absorption spectra of the proposed metamaterial with the nano-cylinder and 30-layer graphene show high absorption (88.3%) in the range of 250-2300 nm, which covers the entire solar spectrum. Moreover, the graphene-based metamaterial has a low thermal emittance of 3.3% in the mid-infrared range (4-13 µm), which can greatly reduce the heat loss. The proposed metamaterial has a tunable cutoff wavelength, which can be tuned by controlling the Fermi level of graphene. In addition, our structure is an angle-insensitive absorber, and the device has the potential to be widely used in solar cell and thermal detectors.