The present application discloses a sizing method for making paper. An alkenyl succinic anhydride (ASA) is added to a papermaking process. An aluminum salt is added in one or more process steps during the papermaking process. Preferably, the aluminum salt is an aluminum salt which can generate free aluminum ion in aqueous solution. The sizing method of the present application enhances the usage efficiency of a sizing agent and the aluminum salt, as well as provides paper having a high moisture content.