Abstract: Ceramic matrix composites (CMC) are prone to internal defects during manufacturing, which significantly affect their performance. Ultrasonic detection has been widely used for detecting such defects. However, the numerous woven pores within CMC cause severe attenuation of ultrasonic waves, particularly at high frequencies. To ensure adequate signal penetration, lower frequencies are often employed, although this compromises the accuracy of defect detection. This study employed finite element simulations to analyze the propagation characteristics and acoustic field distributions of three different low-frequency ultrasonic waves in CMC, with the goal of identifying the optimal frequency for detecting delamination defects. The finite element results demonstrate that, compared to 0.5 MHz and 2 MHz, 1 MHz ultrasound effectively reduces scattering effects while enhancing detection accuracy. Subsequently, SiC_f/SiC CMC specimens with artificial defects were inspected using the selected frequency. Results indicate that 1 MHz ultrasound effectively reduces attenuation and interference with ultrasonic signals caused by the woven pores within CMC, enabling reliable detection of delamination defects larger than 2 mm.