Compound substrate, preparation method of compound substrate and preparation method of light emitting diode chip

The invention discloses a compound substrate, a preparation method of the compound substrate, and a preparation method of a light emitting diode chip with a vertical structure based on the compound substrate. According to the compound substrate, the thickness of a first gallium nitride layer clamped between a first graph layer and a second graph layer is less than the height of first bulge structures, so that the first bulge structures on the first graph layer can be connected with and communicate with the second bulge structures on the second graph layer; and the second bulge structures on the second graph layer are connected together, so that the first graph layer and the second graph layer can form a whole mutually connected graph capable of being corroded with a wet corrosive solution. Once the wet corrosive solution begins to corrode the graph layers from the side face of the compound substrate, the wet corrosive solution can permeate and etch each bulge structure better, so that the wet corrosion stripp