High volume fraction SiC nanowires-reinforced SiC composites (SiCNWs/SiC) were prepared by hybrid process of chemical vapor infiltration and polymer impregnation/pyrolysis in this research. SiCNWs networks are first to be made promising a high volume fraction (20vol%), and the pyrolytic carbon (PyC) interphase with 5nm is designed on SiCNWs surface to optimize the bonding condition between SiCNWs and SiC matrix. Nanoindentation shows a modulus of 494 +/- 14GPa of SiCNWs/SiC composites without interphase comparing to the one with PyC interphase of 452 +/- 13GPa. However, the 3-point bending test shows a higher strength of the composite with PyC interphase (273 +/- 32MPa) comparing with the one without interphase (240 +/- 38MPa). The fracture surface is observed under SEM, which shows a longer SiCNWs pullout of the composite with PyC interphase. The energy dissipation during the 3-point bending test is calculated by the length of nanowire pull-out, it demonstrates that the SiCNWs with PyC interphase possess better performance for toughening composite. Further characterization proves that the PyC interphase can give SiCNWs/SiC composites higher fracture toughness (4.49 +/- 0.44MPam(1/2)) than the composites without interphase (3.66 +/- 0.28MPam(1/2)).