In this paper, a large aperture medium-wave (3~4.5 μm) acousto-optic tunable filter using tellurium oxide crystal as acousto-optic medium material is introduced in this paper. Through optimizing the design,its clear aperture has reached 20 mm×20 mm,and its luminous flux has increased by 3 times compared with the commonly used acousto-optic tunable filters (optical aperture 10 mm×10 mm).This acousto-optic tunable filter is designed for the incident o-light, which adopts a single-chip transducer structure. The results show that through design optimization, the filter achieves a filter range of 3.0~4.5 μm,a separation angle of 5.25°,a diffraction efficiency of greater than 60%,and a spectral resolution of less than 45 nm.