The invention relates to a gallium nitride (GaN)-based light-emitting diode (LED) epitaxy structure, in particular to the GaN-based LED epitaxy structure and a preparation method of the structure, aiming at solving the problems that the existing GaN-based LED epitaxy structure is lower in luminous efficiency, poorer in photoelectric property and lower in yield. The GaN-based LED epitaxy structure comprises a sapphire substrate, a low-temperature GaN buffer layer, an undoped GaN layer, an n-type doped GaN layer, a superlattice layer, a multiple-quantum well luminous layer, a p-type AlGaN layer and a p-type GaN contact layer, wherein the low-temperature GaN buffer layer grows on the upper surface of the sapphire substrate; the undoped GaN layer grows on the upper surface of the low-temperature GaN buffer layer; the n-type doped GaN layer grows on the upper surface of the undoped GaN layer; the superlattice layer grows on the upper surface of the n-type doped GaN layer; the multiple-quantum well luminous layer grows on the upper surface of the superlattice layer. The GaN-based LED epitaxy structure and the preparation method of the structure are suitable for manufacturing a semiconductor luminescent device.