SiC nanowire porous layer was synthesized in situ by a simple two-step technique involving slurry painting and high temperature heat-treatment without catalyst assist. The proposed method is effective and low-cost, which can prepare plentiful and high-purity SiC nanowires (SiCNWs). The microstructure of SiCNWs and the effects of heat-treatment temperatures on the synthesis of SiCNWs were investigated in detail. Results show that the as-synthesized NWs consisted of 3C-SiC, with the length of up to several hundred micrometers and the diameter of 50-100 nm at 1500 degrees C. Meanwhile, the diameter of SiCNW increases with the increasing of heat-treatment temperature. The growth process of the SiCNWs can be controlled by the vapor-solid growth mechanism. After introducing SiCNWs into the SiC coating prepared by pack cementation, the elastic modulus of the nanowire-toughened SiC coating was increased by 35% compared to SiC coating without SiCNWs.