A method of extracting Flavonoid compound from the cactus plant, which includes extraction of cactus by the auxiliary solvent with the ratio of the cactus to the auxiliary solvent at 1:2 and 1:5 in weight percentage the mixture of the auxiliary solvent and the cactus is then placed into the extraction trough whose temperature is set at 35 to 60 DEG C supercritical fluid is passed into the extraction trough, wherein the supercritical fluid of the present invention is the carbon dioxide, and the pressure in the control systems of the air pressure regulator and the back pressure regulator is adjusted to control the pressure in the extraction trough to be 1,500 to 3,500 psi reaction for a period of time releasing pressure to the normal pressure and staring to collect the initial extract of Flavonoid under the normal temperature drying under 105 DEG C, the collected initial extract of Flavonoid to obtain the material as the Flavonoid compound.
