Experimental method was used to investigate the tensile failure modes of two different C/C composites bolts in this paper.Test results indicated that the failure modes were determined by the type of the structure of the bolt head. For the shear failure of the bolt head caused by the tensile load,the comprehensive effect of both the interlaminar and intralaminar shear load is the main factor, but not a single shear load.As a result,improve the design of the structure of the bolt head can enhance the strength of the composites.