Abstract: This paper deals with the fracture of carbon/aluminum composites undef lower stress which means the tensile strength of composite is lower than ROM value and the fiber did not play its reinforcing effect sufficiently. In order to investigate the variation of tensile strength of C/A1 composites as a result of different degrees of interfacial reaction and states of interface, different treatments have been conducted for M40/LD2, T300/LD2, Cs/LD2 composites, which are treated by thermal cycling from liquid nitrogen temperature to 150℃ and heat treated at 300-600℃ under vacuum. It is found that the interface reaction, damage of fiber, strong or weak interface bonding obviously influence the fracture process and strength of C/A1 composite. The interface bonding of C/A1 composite can be controlled and improved by suitable treatment, and the tensile strength of M40/LD2 composite may increase by 25-40%. The control of interface state of composite is the key for producing high quality C/A1 composites.