Large-scale ultra-long 6H-SiC nanowires were in situ synthesized on the as-prepared SiC-Si ceramic substrate using graphite as the carbon source and substrate as the silicon source via improving the adsorbed O-2 content on the graphite precursors using milling technology. The as-grown nanowires were typical single crystal of hexagonal 6H-SiC with diameters of 50-100 nm and lengths of up to several millimeters (or even centimeters). Vapor-solid mechanism was proposed for the growth mode of the as-grown ultra-long 6H-SiC nanowires. This study not only provided new insight into the growth mode for in situ synthesizing 6H-SiC nanowires on silicon-based ceramics, but also suggested a new design methodology for synthesizing ultra-long nanowires.