The present invention provides a method for preparing a pharmaceutical composition comprising a quinoline derivative or a salt thereof. Specifically, the invention provides a method for preparing a pharmaceutical composition comprising an (R, E)-N-(4-(3-chloro-4-(pyridin-2-ylmethoxy)phenylamino)-3-cyano-7-ethoxyquinolin-6-yl)-3-(1-methylpyrrolidin-2-yl)-propeneamide or a pharmaceutically acceptable salt thereof. The method comprises using a wetting agent comprising at least one organic solvent for a wet granulation in a preparation process of the pharmaceutical composition. The pharmaceutical composition prepared using the method has a uniform distribution of grain sizes during the preparation process and a property of rapid and uniform dissolution.