Whispering-gallery-mode (WGM) optical microcavity acoustic sensors have attracted extensive attention owing to their high sensitivity, broad bandwidth, miniaturization and anti-electromagnetic interference capability. This review systematically surveys medium-adapted acoustic sensing and function extension applications of WGM microcavities. Starting from perturbation theory, we distinguish between optical quality factor Q₀ and mechanical quality factor Q_m, and elucidate the intrinsic sensitivity–bandwidth trade-off dominated by mechanical dynamics. We summarize advances in air-coupled and liquid-phase acoustic detection, photoacoustic imaging, and multiparameter multifunctional sensing. Practical bottlenecks including calibration deficiency, thermal drift-induced crosstalk, packaging trade-offs, long-term stability and array scalability are analyzed. Joint hardware–process–algorithm optimization strategies are discussed, providing references for advancing WGM microcavity acoustic sensors toward real-world engineering deployment.