In order to discover the underlying mechanisms of tensile fracture of composites,the tensile mechanical properties of graphene /SiC composites are simulated on the basis of molecular dynamics ( MD) .The results show that ( 1) the interface between graphene and SiC may affect the mechanical properties of the whole composite systems; ( 2) in comparison with the damage of bulk SiC systems,the damage of the composites tends to nucleate and grow on the interface in the tension process; ( 3) graphene /SiC composites with different interface structures possess different mechanical behaviors due to the various interaction between graphene and SiC; and ( 4) in comparison with the contact of grapheme sheet with C surface,the direct contact of single graphene sheet with Si in the substrate results in higher strength and failure strain.