Improved sizing agent for paper or paperboard and preparation method thereof

The invention discloses an improved sizing agent for paper or paperboard and a preparation method thereof, and the preparation method comprises the following steps: (1) treating starch with acetic anhydride to finally obtain a first starch treatment substance; (2) under an alkaline condition, adding epoxy bromopropane to treat the first starch treatment substance, so as to obtain a second starch treatment substance; (3) heating and refluxing under the action of ethidene diamine and ammonia water to obtain aminated starch; (4) carrying out epoxidation reaction to obtain epoxy calcium succinate; (5) mixing calcium epoxysuccinate with the third starch treatment substance for reaction to obtain modified starch; and (6) mixing the modified starch with ingredients to obtain the sizing agent. The modified starch prepared by the invention is used as a sizing agent, can give consideration to water resistance and paper surface strength at the same time, also avoids the phenomena of powder falling and falling of traditi