The invention discloses a desulfurization absorbent for deeply desulfurizing refined diesel oil. The desulfurization absorbent is prepared by the following steps: washing and drying rice husks; crushing the rice husks and carbonizing the crushed rice husks in a muffle furnace to obtain rice husk ash; adding the rice husk ash into a water solution of inorganic alkali; standing for 12-36 hours at 100 DEG C; then putting the mixture into the muffle furnace, roasting and activating; after cooling, washing the mixture to be neutral with de-ionized water; drying at 100-130 DEG C; and grinding to obtain the unmodified desulfurization absorbent. The invention also discloses a preparation method of the desulfurization absorbent. The desulfurization absorbent has large specific surface area, ideal distribution of pore volume and pore diameter and high content of strong acid radicals; the effective adsorption capacity to DBT sulfur is 25.48mgS/g-38.62mgS/g; the desulfurization activity is high and the desulfurization effect on dibenzothiophene organic sulfides is especially high; and the requirements on production of low-sulfur or ultralow-sulfur diesel oil are met.