The present invention discloses a two-dimensional AlN material and its preparation method and application, wherein the preparation method comprises the following steps: (1) selecting a substrate and its crystal orientation; (2) cleaning the surface of the substrate; (3) transferring a graphene layer to the substrate layer; (4) annealing the substrate; (5) using the MOCVD process to introduce H2 to open the graphene layer and passivate the surface of the substrate; and (6) using the MOCVD process to grow a two-dimensional AlN layer. The preparation method of the present invention has the advantages that the process is simple, time saving and efficient. Besides, the two-dimensional AlN material prepared by the present invention can be widely used in HEMT devices, deep ultraviolet detectors or deep ultraviolet LEDs, and other fields.