The invention discloses an application of alantolactone in preparation of medicines for resisting cryptosporidium parvum. The application method comprises the following steps: preparing powder from alantolactone and acceptable auxiliary materials; adding to a feed, mixing evenly, and feeding mouse according to the daily feed amount; or preparing an alantolactone water-soluble power from the alantolactone, dissolving into water, and feeding the mouse according to the daily water consumption. An animal infection experiment proves that the oocysts after cryptosporidium parvum injection can be reduced by 75% or above by the alantolactone; and the alantolactone has a relatively good effect of resisting cryptosporidium parvum.