The present invention relates to a preparation method of formaldehyde-free dye-fixing agent. Said method includes the following steps: (1), adding (by weight portion) 40-50 portions of ethyl acrylate, 1-2 portions of acrylic acid and 60-65 portions of sodium metabisulfite into a reaction still, stirring and uniformly mixing them, heating to 65 plus or minus 2 deg.C, heat-insulating and making reaction for 2 hr plus or minus 0.5 hr; (2), drop-adding 80-85 portions of di-ethylene triamine and controlling temperature below 70 deg.C; (3), adding proper quantity of water, after 10 min, drop-adding 70-75 portions of epichlorohydrin and controlling temperature below 70 deg.C so as to produce transparent or light yellow color, cooling; and (4), cooling to room temperature, adding concentrated hydrochloric acid to regulate pH value and make it be 6-7, regulating solid content so as to obtain the invented finished product. |