Abstract: The braided C/SiC composites with density of 1.65 g/cm³, 1.75 g/cm³ and 1.85 g/cm³ were tested to obtain the basic mechanical properties. The acoustic emission system was used to monitor the damage signals of the monotonic tensile test, and the characteristic parameter and K-cluster analysis of the acoustic emission signals after the noise reduction using wavelet method were analyzed. The difference of material density between the material damage mode, damage evolution process and failure modes was found by the analysis of SEM image. According to the distribution characteristics of the damage mode and acoustic emission events, the experimental acoustic emission signals were classified and analyzed, and the damage modes and damage evolution mechanisms of different density materials were studied, and the stress level, relative time and frequency of different damage modes are gradually increased with the increase of density. It is concluded that the material density can change the mechanical properties by influencing the damage degree and distribution area of matrix as well as the interfacial properties.