The invention discloses a quantum dot light emitting diode and a preparation method thereof, wherein the quantum dot light emitting diode comprises a cathode, an anode and a quantum dot light emitting layer arranged between the cathode and the anode, and the quantum dot light emitting layer is made of materials. It is a mixed material composed of quantum dots and oil-soluble PAMAM dendrimers, and the exciton Bohr radius of the quantum dots is larger than the diameter of the quantum dots. In the present invention, the spatial distance between the quantum dots in the quantum dot light-emitting layer will be effectively pulled apart by the oil-soluble PAMAM dendrimers, thereby effectively reducing the energy transfer between the quantum dots, and indirectly improving the The fluorescence intensity of the quantum dot light-emitting layer; in addition, the oil-soluble PAMAM dendrimer can be wrapped on the surface of the quantum dot to bind the excitons, thereby improving the quantum yield of the quantum dot light-emitting layer, thereby improving the quantum dot light-emitting diode. Luminous efficiency.