Abstract: Based on the Christoffel equation, using the relationship between the composite stiffness matrix and the elastic constant, the orthotropic model was applied to the acoustic properties of 2D-C/SiC composites, and the expression of the material sound velocity was obtained. Through the cyclic loading and unloading test, the sound velocity changes at different stress levels during the entire tensile process were measured. The damage characterization of the sound velocity on the 2D-C/SiC composite was studied. The results show that as the stress level continues to increase, the sound velocity gradually decreases, and the material The degree of damage has a greater impact on the propagation speed of sound waves in the 2D-C/SiC composite; the unloading modulus and reloading modulus are introduced to replace the sound velocity theory to calculate the tangent modulus. It is found that the theoretical results are in good agreement with the test results, and the error increases with the increase of load; The sound wave velocity decreases with the damage of the 2D-C/SiC composite, and based on this attenuation relationship, the damage characterization based on the sound velocity was established.