Abstract: A patterned aluminum nitride (AlN) composite substrate and a preparation method thereof are provided. A single crystal AlN with a semi-suspended AlN structure is prepared on a high temperature-resistant substrate. A non-suspended AlN of the single crystal AlN is covered by an optical medium material while a suspended AlN is exposed. A surface of the suspended AlN with a low dislocation density and a low mismatch stress and distributed periodically is used as a nucleation growth zone of a nitride semiconductor. An epitaxial interface is changed from an AlN/high temperature-resistant substrate into a homogeneous or nearly-homogeneous interface between the nitride semiconductor and the AlN. In this way, the patterned AlN composite substrate is obtained.