Rhizoma Drynariae extract (RDE) is used as therapeutical agent or in the preparation for Osteoporosis, which is characterized in containing over 30 percent of total flavonoids. Furthermore naringin contained in flavonoids is more than 30 percent and less than 100 percent. The RDE is applied for the therapy of osteoporosis or used for producing drugs treating osteoporosis. And methods of extracting the same are also related.