The invention relates to the technical field of compound purification, and particularly provides a purification method of dialkyl methylphosphite. The purification method comprises the following steps: adding a weak polar
solvent into a reaction solution containing dialkyl methylphosphite,
magnesium chloride and an
ether solvent, conducting cooling to -10 DEG C to 40 DEG C, adding a
nitrogen-containing organic alkali compound, carrying out a heat preservation reaction, and conducting filtering to obtain
magnesium chloride and a filtrate; and rectifying the filtrate to obtain a dialkyl methylphosphite product. According to the purification method provided by the invention, the purity and the yield of the dialkyl methylphosphite are improved, the obtained
magnesium chloride does not containcrystal water, the
nitrogen content in the magnesium chloride is 0.01-0.5%, and the purity of the
anhydrous magnesium chloride can reach 97% or above; and the purity of the obtained dialkyl methylphosphite product can reach 97% or above, and the yield can reach 85% or above. The method has the advantages of simple process, no need of special equipment, mild
reaction conditions and no need of high-temperature
distillation or low-temperature brine treatment process, and is suitable for large-scale industrial production.