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 materi als, and the design of sensing structures. The article begins by elucidating the fundamental concepts of piezoelectric ity, 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 proper ties. Subsequently, the article thoroughly analyzes sensing structures like cantilever beams and thin films, which ef ficiently 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, detai ling their working principles and applications across various domains. Finally, the article summarizes the applica tions of MEMS acoustic devices in fields such as consumer electronics, industrial inspection, environmental monito ring, military, and medical applications, and provides an outlook on their future development trends.