The present application discloses a gallium arsenide single crystal and preparation method thereof. The gallium arsenide single crystal has a carrier concentration of 1×1018-4×1018/cm3, and a migration rate of 1700-2600 cm2/v·s; at a same carrier concentration, B atom density in the gallium arsenide single crystal obtained using SixAsy compound as a dopant is at least 20% lower than that obtained using Si substance as a dopant; B content in the gallium arsenide single crystal is 5×1018/cm3 or lower. The preparation method for the gallium arsenide single crystal is that, before growth of the gallium arsenide single crystal, the SixAsy compound is distributed into a gallium arsenide polycrystal.