The invention discloses a preparation method of a light emitting diode epitaxial wafer, and belongs to the technical field of a semiconductor. The preparation method comprises the steps of providing an AlN sapphire substrate; enabling a non-doped gallium nitride layer to be grown on the AlN sapphire substrate; enabling an N type gallium nitride layer to be grown on the non-doped gallium nitride layer; enabling a multi-quantum-well layer to be grown on the N type gallium nitride layer; enabling an electron barrier layer to be grown on the multi-quantum-well layer; and enabling a P type galliumnitride layer to be grown on the electron barrier layer, wherein the electron barrier layer is a P type doped aluminum gallium nitrogen layer; and the surface, for growing the P type gallium nitride layer, of the electron barrier layer is a nitrogen polarized surface. By setting the surface, with the P type gallium nitride layer, of the electron barrier layer into the nitrogen polarized surface, the contact between the electron barrier layer and the P type gallium nitride layer is closer due to the fact that the nitrogen polarized surface is more uneven in a concave and convex manner than themetal polarized surface, so that the ohmic contact resistance is low, the short channel effect is weak, hole injection can be promoted, the recombination efficiency of holes and electrons can be improved, and the luminous efficiency of the light emitting diode is improved.