Using 3D carbon fibre preform, with C3H6 as the carbon source and N2 as the carrier gas, C/C composites are fabricated by the fast CVI process. The effects of heat-treatment on flexural strength, fracture ways and the uniformity of C/C composites are analyzed under different CVI processes. The experimental results indicate that the fracture characteristics of composites are closely related to the times of heat-treatment during CVI process. Compared with a continuous CVI, C/C composites show a pseudo-plastic fracture with the destiny 1.8 g/cm3 and flexural strength 196.69 MPa after two "CVI-heat treatment" circulation under multi-stage CVI process, and the uniformity of materials is well by Weibull distribution.