An injection stimulation agent for water injection well and the preparation method and application thereof are described. The raw material composition of the injection stimulation agent for water injection well comprises: 5.0%-10.0% of sulfamic acid, 10.0%-20.0% of methanol, 10.0%-20.0% of tartaric acid, 10.0%-20.0% of ethylenediamine tetramethylene phosphoric acid, 5.0%-10.0% of sodium polyacrylate, 5.0%-8.0% of cocoyl hydroxyethyl sulfonic acid and the balance of water. Embodiments include a preparation method of the above injection stimulation agent. The injection stimulation agent for water injection well can be used in acidizing treatment process of the reservoir, and can be used directly. The injection stimulation agent can play the role of shrinking swelled clay at the same time of dissolving scale, and finally achieve the purpose of depressurization and enhanced production.