The thermal shock behavior of a three-dimensional carbon fiber reinforced SiC matrix fabricated by chemical vapor infiltration (CVI) technique was studied using the air quenched method. Damage to composites was assessed by a destructive technique of measuring mechanical properties using three-point flexure and SEM characterization. C/SiC composites displayed good resistance to thermal shock, and retained 83% of the original strength after quenching from 1300 to 3008C 100 times. The critical DT of C/SiC in combustion environment was 7008C. The critical number of thermal shocks for the C/SiC composite was about 50 times. When the number of thermal shocks was less than 50 times, the residual flexural strength of C/SiC composites decreased with the increase of thermal shock times. When the number of thermal shocks of C/SiC was greater than 50, the strength of C/SiC did not further decrease because the crack density was saturated.