The invention relates to a preparation method of a PVA (Polyvinyl Acetate) / PEI (Polyethylenimine)-T nanofiber membrane capable of specifically adsorbing mercury ions. The preparation method comprises the following steps of: (1) dissolving thymine-1-acetic acid into water, adding EDC (Ethylene Dichloride), stirring for 2-5hours to obtain a solution, then adding a PEI solution, reacting through stirring, and carrying out dialyzing and freeze drying to obtain PEI-T; and (2) mixing a PVA aqueous solution and the PEI-T to obtain a polyvinyl alcohol PVA / PEI-T solution, and carrying out electrostatic spinning, glutaraldehyde steam crosslinking, rinsing and vacuum drying to obtain the PVA / PEI-T nanofiber membrane. A using method of the PVA / PEI-T nanofiber membrane comprises the following steps of: adding a pH buffer solution of mercuric salts into the PVA / PEI-T nanofiber membrane, carrying out adsorption under the condition of room temperature, sampling, and testing the variation of the concentration of the mercury ions. According to the preparation method disclosed by the invention, the preparation process is simple and is easy to operate, the stability of fiber materials water is good, the fiber materials water is convenient to recover and is high in repeated utilization ratio, and the mercury ions have high specific adsorption.