A numerical simulation of a metamaterial broadband absorber is performed using the finite-difference time-domain method. The absorber adopts a four-layer structure with titanium dioxide (TiO₂) rectangular pairs, a bismuth (Bi) layer, a silicon dioxide (SiO₂) layer, and a titanium nitride (TiN) layer from top to bottom, respectively, and the TiO₂ rectangular pairs are periodically and symmetrically arranged in a rectangular array. The optimization results show that the average absorption of the designed absorber is 97.6% in the wavelength range of 500 to 3500 nm and the average absorption can reach 99% in the wavelength range of 811 to 3162 nm (2351 nm). The coupling of local surface plasmon resonance and propagating plasmon resonance and the good absorption and broadband absorption properties exhibited by metallic Bi were further found by analyzing the distribution of electromagnetic fields. The designed absorber has polarization and temperature-insensitive properties and a simple structure and is easily fabricated.