The invention discloses starch grafted acrylamide and a preparation method and application thereof. The preparation method comprises the following steps: preparing waxy corn starch milk and adding an expansion inhibitor; adding alkali to adjust the starch milk to a certain pH value, adding a cationic reagent, and performing a cationic reaction at the temperature of 70-90 DEG C; taking acrylamide as a monomer, adding an initiating agent, performing a graft copolymerization reaction in a water phase of 40-80 DEG C, separating, drying and smashing to obtain the starch grafted acrylamide. By adding the prepared starch grafted acrylamide into the wet part of a papermaking machine in a certain mass ratio, the physical strength of produced paper can be enhanced.