A simple, direct synthesis method is used to grow core-shell Si-SiO2 nanowires by heating NiO catalyzed silicon substrate. The main crystal growth directions of the Si and SiC nanowires were [111]. The morphology of nanowires was controlled by carbothermal reduction of WO3 and C, which provides reductive environment to synthesize crystalline Si and SiC nanowires covered with SiO2 sheath in the growth temperature of 1000-1100℃. After hydrofluoric acid (HF) treatment, the single crystalline silicon and silicon carbide nanowires were obtained. A solid-liquid-solide(SLS) mechanism is proposed for the growth of both core-shell Si-SiO2 and SiC-SiO2 nanowires. the field emission properties of the syntehsized nanowires directly grown from NiO/Si substrate are reported.