The invention relates to a preparation method and application of ferritin-metal nanoparticles. The method comprises the following steps: preparing a ferritin cage, loading metal ions and forming the ferritin-metal nanoparticles. According to the ferritin-metal nanoparticles prepared by the preparation method, the diameter is about 10 nm; each nanoparticle contains about 150 metal ions. The ferritin-metal nanoparticles provided by the invention can be used for effectively inhibiting tumor metastasis; when the ferritin-metal nanoparticles are combined with ascorbic acid, tumor cells can be selectively killed and the tumor growth is inhibited.