Effects of the KCl additions (1%, 3%, 5% and 7% of the phenolic resin mass) on phase composition and microstructure of the resin carbon and the growth mechanism of carbon fibers were investigated by using commercial liquid phenolic resin as carbon source and micron-scaled KCl as catalyzer, mixing, hexamethylenetetramine solidification treating, carbon-embedded firing at 1 000 ¡æ for 3 h in order to accelerate the graphitization of phenolic resin during carbonization. The results show that the graphitization degree of resin carbon is improved by catalysis of KCl, numerous carbon fibers with 30-200 nm in diameter and 10-20 μm in length and sheetª²like carbon in situ grow in resin carbon. The optimal addition of KCl is 5% when lots of carbon fibers can be found in resin carbon, and d002 diffraction peak of graphite appears obviously in the XRD pattern. The growth mechanism of carbon fiber is that the molten KCl at high temperatures absorbs carbonaceous gas from the decomposition of phenolic resin, accelerating the diffusion of solid C atoms in liquid KCl; after the dissolution of C saturates, carbon atoms separate continuously in local parts to form carbon fibers or flakes; meanwhile, the concentration gradient formed by local carbon atoms in the melt offers growth drive for the separation of carbon fibers or flakes on KCl surface.