Fiber optic Fabry-Perot sensor technology offers numerous advantages for ultrasonic detection. However, demodulating the ultrasonic frequency band of the Fabry-Perot sensor is challenging, owing to complex external environments and existing technical limitations. Thus, the fast and stable demodulation of ultrasonic sensor information a key issue. First, this study introduces the development and principles of the Fabry-Perot ultrasonic sensor. Second, this study deeply analyzes the method principles, research progress, and existing problems in the demodulation process of the fiber optic Fabry-Perot ultrasonic sensor, and proposes application limitations for various demodulation methods. Finally, this study provides a prospective summary of demodulation methods for Fabry-Perot ultrasonic fibers.