The invention provides an acanthopanax effective constituent, which mainly comprises compound A of Anhydrochiisanogenoic acid and compound B of Oplopanaxogenin A; wherein, 50% to 70% A and 20% to 40% B are contained. Medicinal materials are heated and extracted, concentrated, separated by silica gel column, eluted; the eluate is concentrated and dried, and then separated by liquid phase chromatogram; the solution is connected, concentrated and dried for an effective constituent. The acanthopanax effective constituent can be used for preparing the medicines for curing and preventing tumor. Theinvention has a reasonably designed method, can get the effective constituent quickly and exactly, and is easier to control the medicine quality on stream.