The invention discloses an LED purple light epitaxial structure of a vertical structure and a preparation method thereof. The preparation method comprises the following steps: using ammonia gas, high-purity trimethyl indium (TMIn), TMAl, TEGa and high-purity trimethyl gallium (TMGa) as sources respectively, using SiH4 and Cp2Mg as an n-type doping agent and a p-type doping agent respectively, using hydrogen or nitrogen as carrier gas, introducing the carrier gas into a reaction chamber to perform a chemical reaction with the ammonia gas at the temperature of 900-1100 DEG C, generating a three-five compound semiconductor, and depositing on sapphire, a silicon wafer, a silicon carbide sheet or a quartz glass sheet according to a certain lattice sequence to prepare the epitaxial structure. The components, doping concentration, thickness and the like of the epitaxial layer can be controlled by accurately controlling the flow and on-off time of a gas source, the regulating range of growth rate is relatively wide, and the relatively high growth rate can be applicable to batch growth.