The invention discloses a light-emitting diode epitaxial wafer and the preparation method thereof, and belongs to the semiconductor technology field. The epitaxial wafer comprises a substrate, a buffer layer, a non-doped gallium nitride layer, an N-type gallium nitride layer, a multiple quantum well layer, an electron blocking layer, and a P-type gallium nitride layer. The multiple quantum well layer comprises a plurality of quantum well layers and a plurality of quantum barrier layers, which are in an alternately-laminated arrangement. The quantum barrier layers comprise n+1 first sub-layers and n second sub-layers, which are in an alternately-laminated arrangement, and n is a positive integer. The first sub-layers are non-doped gallium nitride layers, and the second sub-layers are gallium nitride layers doped with silicon. The layers doped with the silicon and the non-doped layers are alternately grown, and current expansion is effectively enhanced, and a part of silicon of the gallium nitride layers doped with silicon can permeate into the non-doped gallium nitride layers, and therefore the light-emitting efficiency and the brightness of the LED are guaranteed, and line defects are reduced, and voltage is lowered.