A metamaterial-based optical solar reflector (OSR) consisting of a three-layer structure of aluminum-doped zinc oxide (AZO) metasurface, a MgF₂ dielectric layer and an Ag metal reflector layer is investigated. In the thermal infrared, the AZO metasurface excites the surface equipartition excitation resonance to enhance the electromagnetic absorption, the stability of the MgF₂ dielectric constant reduces the reflection caused by the absorption oscillations. In the visible light, the transparent properties of AZO and MgF₂ provide the low loss for the solar radiation, and the Ag reflector layer effectively suppresses the transmission. Simulation results show that the optimized OSR has a low solar absorptivity of 17.6% in 0.3~2.5 µm and a high IR emissivity of 86.5% in 2.5~30 µm. In addition, polarization and angle of incidence have a small effect on its performance. The structure achieves good absorption in the infrared band and also has potential applications in infrared thermography, radiative cooling, and other fields.