The invention belongs to the field of herbal cosmetic additives and discloses an apocynum venetum extract, a preparation method thereof and application thereof to cosmetics. The apocynum venetum extract is prepared by the following steps of: removing impurities from dogbane leaves and washing the dogbane leaves; performing continuous countercurrent extraction for 30 to 90 minutes at the temperature of between 45 and 70 DEG C and then filtering to obtain filtrate, wherein the weight ratio of the dogbane leaves based on the dried weight to water is 1:8 to 1:20; adding a chitosan flocculating agent into the filtrate, standing, performing centrifugation and removing precipitates to obtain the clear solution of an extract; performing vacuum concentration; washing macroporous resins on the concentrated solution with distilled water to colorless; performing elution with ethanol at the concentration of 20 to 85 percent; detecting the eluent and collecting active ingredients; and spray drying to obtain the apocynum venetum extract with the total flavonoid content of over 30 percent. The apocynum venetum extract can be applied to developing functional cosmetics with effects of skin peroxidation resistance, senility delay, whitening, radiation resistance, sun protection, inflammation resistance, allergic resistance, bacterial inhibition, moistening, moisture maintenance and the like.