Currently, underwater ultrasonic testing places higher demands on the structural size, sensitivity, and reliability of ultrasonic probes. This article proposes a method for designing and fabricating a capacitive micromechanical ultrasonic transducer（CMUT） based on cavity SOI technology and completes CMUT electrical performance testing and underwater performance characterization through packaging. The test results show that the CMUT fabricated using this method achieves higher yield and consistency. Its transmission voltage response level is 169.03 dB, reception sensitivity is −211.31 dB, and relative bandwidth is 121%, demonstrating excellent sensitivity characteristics and directionality （with a −6 dB beam width of 8°）. This novel CMUT fabrication method provides theoretical support and a foundation for future high-density CMUT integration and underwater ultrasonic testing.