The invention provides a preparation method of a sealed water-based polyurethane modified PAE (polyarylether) wet strength agent, which comprises the following steps: carrying out vacuum dehydration on polyalcohol and carboxylic acid chain extender, adding organic solvent and polyisocyanate, reacting in a nitrogen atmosphere to obtain NCO-terminated polyurethane prepolymer, and adding a closing agent to react until the -NCO content is zero to obtain a closed polyurethane prepolymer; mixing polyethylene polyamine, dibasic acid and catalyst to carry out polycondensation reaction, removing the generated water by distillation, cooling to 120-140 DEG C, and adding hot water to obtain a polyamide-imide solution; and sequentially adding water and the closed polyurethane prepolymer into the polyamide-imide solution, dissolving by stirring, adding epoxy chloropropane to react, adding a terminator when the system viscosity reaches 40-100 cps, and regulating the pH value of the system to 3.0-5.0. Compared with the traditional PAE wet strength agent, after the wet strength agent provided by the invention is applied to paper, the dry tensile index, wet tensile index, wet strength retention and folding strength are enhanced.