The invention relates to a nano polymer hydroxymethyl chitosan domestic sewage treatment agent and a treatment method, and relates to the technical field of wastewater treatment. The sewage treatmentagent comprises the following components in parts by weight: 15-25 parts of hydroxymethyl chitosan, 5-10 parts of sodium alginate, 5-10 parts of porous sponge graphene, 25-30 parts of furfural acetoneformaldehyde resin, 15-20 parts of modified alginate based fibers, and the like. According to the modified chitosan-based solution provided by the invention, the fibers are adopted as carriers for forming a modified chitosan-based solution, nano titanium dioxide is grafted on the surface for increasing the surface area ratio of the fibers, inorganic cationic poly silicon fluoride is used on the outer layer with a large surface area, and an electrostatic adsorption is carried out with the organic anionic polyalkene amide, so that the stability and the firmness of the material are ensured on the basis of the large surface area ratio. Through the method, the agent is added for carrying out multi-stage sewage treatment on the domestic sewage, the effect is obvious, and the recycling of waterresources is realized.