Abstract: The oxidation damage evolution law of ceramic matrix composites prepared by chemical vapor infiltration (CVI) process was analyzed. Considering the effects of temperature and oxidation time, prediction models of elastic modulus about fiber and cell were established based on the distribution of microcracks in matrix and the oxidation process of interface, fiber and matrix. The prediction results show that the tensile elastic moduli of carbon fiber (C_f)/SiC and SiC fiber (SiC_f)/SiC composites decrease more obviously with the increase of temperature and oxidation time. The elastic prediction model was verified by the tensile tests of the composites after high temperature oxidation. The error between the prediction results and the test results of SiC_f/SiC composites with BN interphase after oxidation at 1000 ℃ for different time is no more than 2%, and the error between the prediction results and the test results of C_f/SiC composites with PyC interphase after oxidation at 700℃ for different time is no more than 7%.