A polymer-metal oxide complex, comprising a metal oxide particle located at the core and a polymer modified on the surface of the metal oxide particle, the polymer being provided with functional groups capable of bonding with a metal in the metal oxide, the density of the binding sites of the polymer and the surface of the metal oxide particle being greater than two sites/square nanometer. Also disclosed are a preparation method for the polymer-metal oxide complex, and applications of the polymer-metal oxide complex as a nuclear magnetic resonance contrast agent and as an iron supplement. The polymer-metal oxide complex has a significantly extended in vivo circulation time and effectively overcomes the defect that existing contrast agents cause hypersensitivity, which in addition to the superparamagnetic and iron metabolism participation functions of the complex, enables the complex to be applied as a magnetic resonance imaging contrast agent and as an iron supplement treating iron-deficiency anaemia.
