Silicon carbide (SiC) particles were synthesized by carbothermal reaction using HBO3, NH4Cl and nano-SiC as additives, and the effects of three additives on the microstructure of SiC particles were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The three additives didn't affect the structural characteristics of SiC. HBO3 could promote the growth of resulting rod-like SiC, NH4Cl to some extent restricted the formation of rod-like SiC, and nano-SiC promoted the formation of rod-like SiC and decreased the radial size.