The invention discloses a light-emitting diode epitaxial slice and a preparation method thereof, and belongs to the field of light-emitting diodes. The epitaxial slice comprises a substrate, a buffer layer, an N-type layer, a stress release layer, a multiple quantum well layer and a P-type layer, wherein the buffer layer, the N-type layer, the stress release layer, the multiple quantum well layer and the P-type layer sequentially grow on the substrate, the multiple quantum well layer is of a super-lattice structure, each cycle of the multiple quantum well layer includes an InyGa1-yN layer and a GaN layer, 0<y<1, the stress release layer is of a cycle structure, each cycle of the stress release layer includes a GaN layer, an InN layer and an InxGa1-xN layer growing on the InN layer, and 0<x<y. The InGaN layer grows on the InN layer in each cycle of the stress release layer, the formation probability of an In-N bond in the InGaN layer is high in rich In atmosphere, and In atoms can be more easily doped into a lattice to form the InGaN layer with high In component content.