The invention relates to a paper dry strength agent as well as a preparation method and application of the paper dry strength agent, and belongs to the technical field of assistants added into paper pulp. The paper dry strength agent is prepared by polymerizing nonionic biological polysaccharide with a molecular weight of 0.5-2 million, alkenyl carboxylic acid and/or a corresponding carboxylate, alkenyl sulfonic acid and/or a corresponding sulfonate, positive ions and alkenyl amide containing an unsaturated double bond. The preparation method of a retention aid for papermaking comprises the following steps: carrying out polymerization reaction and obtaining a product. The paper dry strength agent prepared by the biological polysaccharide graft copolymerization method provided by the invention is good in use effect and has a wide market prospect and good social and economic benefits.