A method for preparing a label-free aptamer electrochemical sensor of γ-interferon based on a dendrimer/gold nanoparticle/molybdenum disulfide nanocomposite is provided. The nanocomposite is drip-coated on a surface of an electrode to prepare a modified electrode, and a terminal sulfhydryl group of a γ-interferon aptamer chain is connected to the gold nanoparticle via Au—S bond to obtain a nanocomposite-aptamer modified electrode. When γ-interferon is present, the γ-interferon specifically binds to the aptamer chain on the sensor, resulting in the aptamer's hairpin structure being opened and stretched, which can effectively adsorb methylene blue MB in the electrolyte, causing significant enhancement of MB redox signal. A linear relationship between a current intensity of MB oxidation peak and a concentration of the γ-interferon is fitted to construct the label-free aptamer electrochemical sensor of γ-interferon.