The invention discloses an ailanthus degreasing method. The method comprises the following steps that firstly, color-change-prevention pretreatment is carried out, wherein a sodium bicarbonate solution with the concentration ranging from 0.5% to 0.8% is sprayed three times, and the spraying interval is two days to four days; secondly, first-time digesting is carried out, wherein ailanthuses are put into a digester containing alkali liquor with the concentration ranging from 4% to 6% to be digested, the temperature is controlled to range from 30 DEG C to 50 DEG C, and the time is controlled to range from 2 hours to 4 hours; thirdly, the ailanthuses which are subject to treatment in the first step and the second step are put into a digester containing alkali liquor with the concentration ranging from 2% to 4% to be digested, the temperature is controlled to range from 30 DEG C to 50 DEG C, and the time is controlled to range from 2 hours to 4 hours; fourthly, rinsing is carried out, wherein the digested ailanthuses are rinsed with clean water two times to three times, the temperature is controlled to range from 20 DEG C to 40 DEG C, and the rinsing interval is 0.2 hour to 1 hour; and fifthly, drying is carried out, wherein a drying machine is used for drying the ailanthuses, and after the ailanthuses are cooled, the ailanthuses are painted with varnish. The method is low in cost, good in degreasing effect and free of affecting the color of the ailanthuses.