The invention discloses a new application of a chemical component of chemical component used as plant estrogen, in particular relates to an application of an eucommia bark extract in preparing a medicine for treating and / or preventing a disease relevant to the estrogen hyposecretion of a mammal (particularly a human). The invention relates to an application of a composition in preparing a medicine for treating and / or preventing a disease relevant to the estrogen hyposecretion of a mammal (particularly a human), which is selected from one or more of the following components: betulinic acid, genipin, aucubin, pinoresinol diglucoside, syringaresinol diglucoside, abietinol monoglucoside, syringaresinol monoglucoside, wogonin, oroxylin A, baicalein and dihydrochalcone 3-O-beta-D-glucoside and a medicine composition containing the eucommia bark extract or an active component in the eucommia bark extract. The eucommia bark extract and a monomer chemical component in the eucommia bark extracthave the effect of effective plant estrogen.