The invention provides a preparation method of a high-purity
crystal, and particularly relates to a preparation method of a
mesylate lenvatinib crystal C. The preparation method comprises the following steps: 1) dissolving a
lenvatinib free alkali in a good
solvent to obtain a solution of the
lenvatinib free alkali; 2) clarifying and filtering the solution obtained in the step 1), adding
methanesulfonic acid and a poor
solvent I or a solution of
methanesulfonic acid in the poor
solvent I, and carrying out a salt forming reaction to obtain a crude product of the
mesylate lenvatinib; 3) putting the obtained crude product of the
mesylate into a poor solvent II, and pulping to obtain a mesylate
crystal C. The purity of the obtained mesylate crystal C is not lower than 99.5%, the purity of any single
impurity is not higher than 0.10%, and the total
impurity is not higher than 0.5%. The purity of the
lenvatinib mesylate crystal C prepared by the preparation method of the
lenvatinib mesylate crystal C is higher, wherein, the contents of an
impurity A and an impurity B in the
lenvatinib mesylate crystal C are greatly reduced.