This article delves into the applications of Micro-Electro-Mechanical Systems (MEMS) in the field of passive acoustics, with a particular focus on the principles of piezoelectricity, commonly used piezoelectric materials, and the design of sensing structures. The article begins by elucidating the fundamental concepts of piezoelectricity, followed by an introduction to several key piezoelectric materials such as quartz, PZT (lead zirconate titanate), and ZnO (zinc oxide), which are widely employed in MEMS technology due to their superior piezoelectric properties. Subsequently, the article thoroughly analyzes sensing structures like cantilever beams and thin films, which efficiently convert acoustic energy into electrical signals. The article also specifically introduces three representative MEMS acoustic devices: MEMS microphones, MEMS hydrophones, and MEMS acoustic emission sensors, detailing their working principles and applications across various domains. Finally, the article summarizes the applications of MEMS acoustic devices in fields such as consumer electronics, industrial inspection, environmental monitoring, military, and medical applications, and provides an outlook on their future development trends.