The invention relates to the technical field of engineering sealing, in particular to a water injection bag. The water injection bag is in a hollow cylindrical column shape overall. Composite rubber skin is adopted for the outer wall, layers of the composite rubber skin are pasted for connection, rubber is adopted as an inner rubber layer and an outer rubber layer, metal drawing nets are adopted as reinforcing layers, a polyvinyl butyral layer is adopted as an intermediate layer, the polyvinyl butyral layer is arranged between the metal drawing nets to integrate the metal drawing nets into onepart to improve toughness of the metal drawing nets as well as guaranteeing strength. The water injection bag is good in toughness and is high in strength, can expand quickly when filled with water,and can retract immediately when water is discharged, so that reuse is achieved.