Chalcogenide glasses, with their broad infrared transmission window and high acousto-optic figure of merit, represent an ideal medium for low-power high-performance acousto-optic modulators, potentially overcoming the diffraction efficiency and power consumption limitations of acousto-optic modulators based on conventional materials. Ge21Sb18S61 chalcogenide glass, characterized by its wide infrared transparency and high refractive index, was systematically investigated for its thermal, physical, optical, and acoustic properties. Using this glass as acousto-optic medium, a high-performance fiber-coupled acousto-optic modulator was successfully fabricated. Experimental results show that under a radio frequency driving power of 0.52 W, the modulator achieves a diffraction efficiency of 84%, a rise time of 41 ns, and an extinction ratio as high as 61 dB, exhibiting excellent low-power consumption and high-efficiency characteristics. This study provides crucial technical support for the design and development of novel acousto-optic devices, contributing to advancements in high-speed optical communication and fiber sensing applications.