The invention relates to a flower-shaped Au micro-nano structure, a modified electrode, a preparation method and an application thereof. In a synthesis process, the morphology of the flower nanostructure is regulated by regulating of experimental parameters in the synthesis process, and finally nanosheets are self-assembled into the Au micro-nanostructures; a flower-shaped Au nanostructured electrode is used as a working electrode to develop a dopamine sensor; electrochemical data shows that the flower-shaped Au nanostructure can accelerate transmission of electrons on dopamine and the sursurface of the electrode, and reduces overpotential in an electrochemical oxidation process, in a dopamine concentration range of 1.25mu M to 1.07mM, oxidation peak current and concentration are in linearrelationship (R=0.997), and the detection limit is 0.61 mu M. In addition, the synthesized electrochemical sensor has good stability and repeatability; and a new method for actual analysis and detection of the dopamine is provided.