The invention provides an interface-enhanced nano silicon dioxide-modified epoxy resin sizing agent for carbon fiber. The sizing agent is prepared from the following raw materials in parts by weight; 60-80 parts of water, 20-40 parts of nano silicon dioxide-modified epoxy resin and 0.01-6 parts of emulsifier. Compared with a common sizing agent, the sizing agent prepared in the invention contains nano silicon dioxide, the particle size of the nano silicon dioxide is small, and the nano silicon dioxide exists on the surface of the carbon fiber after sizing and can improve the interface strength of the carbon fiber and a resin substrate and improve the mechanical property of a prepared and molded composite material.