A method for preparing a biflavone-cobalt complex includes using the amentoflavone as the ligand and the cobalt ion as the central ion, the amentoflavone-cobalt complex is obtained by reaction, and the structure of the complex is characterized by infrared spectroscopy, UV-vis absorption spectroscopy and high resolution mass spectrometry. Meanwhile, the antitumor and antioxidant activities of the amentoflavone-cobalt complex are studied in the present invention. MTT method shows that the amentoflavone-cobalt complex has better antitumor activity, and the antitumor activity thereof is stronger than that of the amentoflavone. Pyrogallol auto-oxidation method, ABTS method and FRAP method show that the antioxidan activity of the amentoflavone-cobalt complex is stronger than that of the amentoflavone itself. The formation of the flavonoid-cobalt complex enhances the antitumor and anti-oxidation activities of the amentoflavone, and is expected to be used in the development of drugs.