Abstract: Carbon nanotubes (CNTs) were introduced into carbon fiber surface and SiC matrix through electrodeposition and chemical vapor infiltration (CVI) method. Then the C/SiC composites (CNTs-C)/SiC and C/(CNTs-SiC) with CNTs deposited at different phases were obtained. The effects of CNTs deposition phases on the mechanical properties of C/SiC composites were investigated. The tensile strength and fracture mechanisms of C/SiC composites with CNTs deposited at different phases were studied. The results show that compared with C/SiC composite without the addition of CNTs, the tensile strength of (CNTs-C)/SiC composites with CNTs deposited on the surface of carbon fibers increases by 67.3%, and the work of fracture increases by 107.2%. However, the work of fracture of C/(CNTs-SiC) composites which introducing CNTs into the SiC matrix decreases, and the tensile strength only increases by 6.9%, the CNTs does not show significant strengthening and toughening effects. C/(CNTs-SiC) composites have the similar fracture morphology characteristics of traditional C/SiC composites, and both of them have the similar fracture and pullout mechanisms, mostly for carbon fiber strengthening and toughening, and CNTs does not play a significant role.