The invention relates to a preparation method of an amorphous quinoline carboxamide derivative, which comprises dissolving lenvatinib mesylate crystal form C in a tert-butanol / water mixed solvent, stirring, filtering, collecting the filtrate, and freeze-drying to obtain an amorphous . The amorphous obtained by the method has high purity, uniform freeze-drying, fluffy sample appearance, low water content, qualified residual dissolution, little damage to instruments and equipment by the freeze-drying solvent, safe operation and suitable for industrial production, and the obtained amorphous is not stable in the preparation process. Gel phenomenon will occur, and capsules made of amorphous materials have the advantage of fast dissolution.