2D-C/C composites fabricated by rapid densification process-Chemical Liquid-Vaporized Infiltration (CLVI) were heat treated at various high temperatures. And then the mechanism and factors affecting the mechanical properties and fracture modes before and after graphitization were analyzed. Results show that after graphitization, the flexural strength decreases, and the fracture behavior changes from a brittle type of failure to pseudoplastic type, while the interlaminar shear strength increases significantly, but the value of ILSS tends to decrease as increasing heat treatment temperature, and the fracture failure displays larger plastic behavior. The interfacial bonding strength plays an important role in the mechanical behavior.