The invention discloses a preparation method of ultrahigh molecular weight polyethylene protofilament. The method comprises the step of fiber finishing. According to the step of fiber finishing, 1, 1-2 parts by mass of dodecyl trimethyl ammonium sulfate, 2.6 parts by mass of azodiisobutyronitrile, 3.5 parts by mass of sodium carboxymethyl starch and 1.3 parts by mass of nanoscale aluminum hydroxide are added into 34 parts by mass of deionized water to be mixed and stirred to be uniform; 2, 4.2 parts by mass of sodium alkylarysulfonate, 1.7 parts by mass of asbestos ash, 3.6 parts by mass of potassium rhodanide and 2.8 parts by mass of N-methyl-pyrrolidone are slowly added at the same time for continuous stirring till sufficient and uniform mixing is performed to obtain a finishing solution; 3, hydroxyethyl cellulose fiber is padded in the finishing solution, taken out and dried at constant temperature. The preparation method of the ultrahigh molecular weight polyethylene protofilament comprises the step of fiber finishing, and the finished hydroxyethyl cellulose fiber has the excellent antibacterial, anti-flaming and anti-static performance.