Compared with single-phase Y₂O₃ ceramics, Y₂O₃-MgO nanocomposite ceramics exhibit superior mechanical strength, hardness, thermal conductivity, and excellent infrared band transparency, endowing them a good infrared window material. However, harsh mechanical and thermal operating conditions impose stringent requirements on the optical and mechanical properties of infrared window materials. In this study, high-purity Y₂O₃-MgO nanocomposite powder was used as raw material, and Y₂O₃-MgO nanocomposite powders with different ZrO₂ contents, in which Zr⁴⁺ ions accounted for the percentage of Y³⁺ ions at 1%, 3% and 5%, were prepared by adding zirconium nitrate aqueous solution during ball milling. ZrO₂:Y₂O₃-MgO nanocomposite ceramics were fabricated by hot pressing sintering at 1350 ℃ and 35 MPa for 30 min. The influence of ZrO₂ content on the phase, microstructure, infrared transmittance, hardness, and bending strength of nanocomposite ceramics was systematically studied. The results showed that doping ZrO₂ dissolved and uniformly distributed in the Y₂O₃ lattice changed microstructure of Y₂O₃-MgO nanocomposite ceramics and caused lattice distortion, which had a significant impact on the optical and mechanical properties of Y₂O₃-MgO nanocomposite ceramics. The microstructures of ZrO₂:Y₂O₃-MgO nanocomposite ceramics reveal that increasing ZrO₂ content can hinder ceramic densification, resulting in obvious pores in 5%ZrO₂:Y₂O₃-MgO nanocomposite ceramic. Meanwhile, doping ZrO₂ can enhance the hardness and bending strength of Y₂O₃-MgO nanocomposite ceramics, which can be attributed to lattice distortion suppressing the dislocations’ motion. 3%ZrO₂:Y₂O₃-MgO nanocomposite ceramic has a dense microstructure, with a transmittance of ~82% in the range of 3-5 μm, while exhibiting a hardness of 11.43 GPa and a bending strength of 276.67 MPa.