SiC fiber (SiC_f)/SiC composites were modified by SiC nanowires (SiC_nw) grown in-situ on SiC fiber to obtain hierarchical structure. Effects of this hierarchical structure on the properties of composites, such as microstructure, fracture strength and damage evolution, were evaluated. Results show that the introduction of SiC_nw significantly improves the matrix infiltration efficiency. SiC_nw and BN-coated SiC_nw reinforced SiC_f/SiC composites acquire better performance in bending tests by comparison with conventional SiC_f/SiC. SiC_nw coated by BN interphase obviously enhances the strength owing to weak-bonded interface. Besides, results of acoustic emission and Coated Vickers Hardness Impresses reveal that SiC_nw delay early damage evolution at early state and mainly make contribution to hindering and bridging of microcracks, which is further enhanced by BN-coated SiC_nw.