In the present work, β-SiC/SiO2 coaxial nanocables are synthesized in a large area via direct pyrolysis of polymeric precursor method, in which, polycarbosilane acts the single raw material. The morphology, chemical composition and detailed microstructure of the nanocables are characterized. The core of nanocables are single crystalline β-SiC nanowires with diameter of 30 - 60 nm grown along [111] direction. The uniform coating layer is amorphous SiO2 with thickness of 15 nm. Based on the pyrolysis process of polycarbosilane, the Vapor-Liquid-Solid growth mechanism is discussed. Furthermore, field emission measurements show the turn-on field and the threshold field are 3.2 V/μm and 6.5 V/μm, respectively. This study shows that β-SiC/SiO2 coaxial nanocables are promising for field emission display device and other vacuum electronic devices.