The present invention relates to a method for preparing an ultrahigh-purity silicon carbide powder, more particularly to a method for preparing an ultrahigh-purity silicon carbide granular powder by preparing a gel wherein a silicon compound and a carbon compound are uniformly dispersed via a sol-gel process using a liquid state silicon compound and a solid or liquid state carbon compound of varying purities as raw materials, preparing a silicon dioxide-carbon (SiO2—C) composite by pyrolyzing the prepared gel, preparing a silicon carbide-silicon dioxide-carbon (SiC—SiO2—C) composite powder via two-step carbothermal reduction of the prepared silicon dioxide-carbon composite, adding a silicon metal and then conducting carbonization and carbothermal reduction at the same time by heat treating, thereby growing the synthesized silicon carbide particle with an increased yield of the silicon carbide.