The invention provides a preparation method of an antibacterial hydrogel material. The method includes the following steps that under acidic conditions, a monomer and a polyvinyl acetal foam materialare subjected to a grafting reaction in the presence of an oxidizing agent to obtain an antibacterial hydrogel material, wherein the monomer is methacryloyloxyethyl trimethyl ammonium chloride. A water-soluble oxidization-reduction initiating system is used for introducing methacryloyloxyethyl trimethyl ammonium chloride onto the polyvinyl acetal foam, and the material keeps the specific pore structures of polyvinyl acetal foam materials and has excellent antibacterial property. Moreover, the provided preparation method has the characteristics that the reaction condition is mild and the methodis simple and feasible, the preparation period is short, the condition is controllable, the equipment requirement is simple, and large-scale production can be achieved. The experimental results showthat the escherichia coli and staphylococcus aureus inhibiting rate of the prepared antibacterial hydrogel material is more than 99.9%.