The invention relates to a method for growing carbon nanotubes on carbon fibers under the joint action of lignin and a bimetallic catalyst. The method includes steps: step 1, feeding the carbon fibersinto a vertical CVD furnace by winding, feeding nitrogen, and keeping the temperature at 450 DEG C for 1.5h to remove a sizing agent; step 2, electrolyzing, guiding the desized carbon fibers into anelectrolytic bath, washing after electrolysis, and drying, wherein electrolyte refers to NH4H2PO4 aqueous solution; step 3, loading the catalyst, and drying, wherein solutes include ferric nitrate, nickel nitrate and sodium lignosulfonate, and absolute ethyl alcohol serves as a solvent; step 4, guiding the carbon fibers into a tube furnace, feeding N2 and H2, keeping the internal temperature of the furnace at 450 DEG C for 5min to reduce the catalyst, and then guiding the carbon fibers into another tube furnace to enable growth of the carbon nanotubes under conditions that N2, H2 and C2H2 gases are fed into the tube furnace, and the tube growth time is 5min. By adoption of the method, the problem of poor connection between the carbon nanotubes and the carbon fibers can be solved, and accordingly mechanical performances of the treated carbon fibers can be improved.