The invention discloses printing ink used for thermal transfer printing applicable to cotton and wool textiles. The printing ink used for the thermal transfer printing is prepared from a disperse dye composition, filler, a dispersing agent, a crosslinking agent, a cosolvent and a catalyst, wherein the disperse dye composition comprises disperse dyes, biological enzymes, activated carbon fibers, copolymers of polyepichlorohydrin or epichlorohydrin and ethylene oxide and a linear polymer of polysaccharide and a peptide chain, wherein the two polymers realize the best synergistic effect with disperse dyes under the action of the biological enzymes and activated carbon fibers, adsorption capacity of the disperse dyes is effectively enhanced, maximum stability is achieved under the synergistic effect of other fillers and auxiliaries, color fixing rate during the thermal transfer printing is effectively increased, and high temperature decomposition rate of the printing ink is reduced. When the printing ink used for the thermal transfer printing applicable to the cotton and wool textiles is applied to treatment on the cotton and wool fiber textiles, the color fixing rate is relatively high, transfer efficiency is excellent, thermal decomposition is hardly caused, release of harmful substances is avoided, and low carbon and environmental friendliness are realized.