Abstract: The process characteristics of 3D braided composites materials and the types of defects that are prone to occur were introduced. Variety of frequencies of ultrasonic waves were used to detect defects inside the material, and the test results were comprehensively compared and analyzed. The test results showed that although the multi-frequency ultrasonic comprehensive comparison method cannot quantitatively detect the pore distribution inside the material, it can judge the pore distribution in different regions.