The present invention provides a GaN nano-structure array preparation method. A CVD device and a graphene insertion layer and low-temperature GaN buffer layer sublimation method are employed to grow the GaN nano-structure array; a substrate employs sapphire, silicon or quartz glass and GaN/sapphire (silicon), after the substrate is cleaned, the substrate is covered by single layer of multiple layers of graphene films; the substrate covered by the graphene films is putted into a CVD pipe-type tube furnace growth system to start the growth of the GaN nano structure; the GaN buffer layer is grown at the low temperature, the GaN nano array is grown after the temperature rises to a high temperature; the growth temperature of the buffer layer is 500-1000 DEG C, and the nanowire array growth temperature is 1000-1500 DEG C; and the high pure N2 is taken as carrier gas, and the total N2 carrier gas flow is 0.5-5 slm.