The invention discloses a GaN-based vertical structure micro-cavity Micro-LED based on an electroplating technology and a preparation method thereof. The micro-cavity Micro-LED is narrow in light-emitting full width at half maximum and good in light-emitting directivity; thickness of a chip is reduced, and a metal reflector of the p-GaN layer (5) and a dielectric film reflector of the n-GaN layerare used as end faces of a resonant cavity to form a resonant micro-cavity structure in the vertical direction, so side wall light emission is inhibited, front light emission directivity is improved,and the crosstalk effect between adjacent pixels of Micro-LED display is reduced. Meanwhile, the resonant micro-cavity structure selects a specific wavelength, so the light-emitting spectrum is narrowed, the spectral purity is higher, the display threshold of the Micro-LED is improved, a Micro-LED active region of the vertical structure is large in area, and n-GaN light absorption is less, the current expansion is good, the voltage is low, the current density is small, and advantages in the aspects of lighting effect, saturation current and long-term reliability are achieved; and secondly, a Cu substrate has good electrical conductivity and thermal conductivity, and thermal resistance of the chip is small.