Porous design of SiC composites with lightweight, high strength and low thermal conductivity can be obtained by constructing porous silicon carbide nanowires (SiCNWs) network and controlling chemical vapor infiltration (CVI) process. The SiCNWs network with an optimized volume fraction (15.6%) and uniform pore structure was prepared by mixing SiCNWs and polyvinyl alcohol (PVA) firstly. SiCNWs reinforced porous SiC ceramic matrix composite (SiCNWs/SiC) with a small uniform pore can be obtained by controlling the CVI parameters. The morphology of the grown SiC matrix, from the spherical particles to the hexagonal pyramid particles, can be influenced by the CVI parameters, such as temperature and reactive gas concentration. The strength of the SiCNWs/SiC ceramic matrix composites reaches (194.3±21.3) MPa with a porosity of 38.9% and thermal conductivity of (1.9± 0.1) W/(m·K), which shows the toughening effect and low thermal conductivity design.