The invention relates to an active ingredient which has role in inhibiting angiogenesis in cortex albiziae. The active ingredient is a saponin compound which has applications of treatment and prevention of diseases about angiogenesis and anti-tumor angiogenesis, can be used in medicines which can prevents angiogenesis, or can be used as conventional medicine carrier and/or excipient, or is applied in preparation of health-care food or cosmetics for prevention of angiogenesis, so that the invention also provides the preparation method of the active ingredient, which is that the dry tree barks, stem skins, leaves, flowers, seeds, pods, or roots of the cortex albiziae are extracted by organic solvents, organic solvents with water or water; the extracting solution is filtered and condensed into extract; the extract is eluted and separated by a D-101 shape macroporous resin, then the effective groups are collected and are eluted and separated by a silica gel chromatography column, another effective groups are collected and separated by an RP-styrene column so that an effective group is obtained, the solvent is recycled to be an extract which is freezed, dried and then made into drymeal.