Embodiments of the invention disclose an array substrate and a preparation method thereof. The method comprises the steps of forming a dielectric layer on a substrate, forming a metal layer on the surface of the dielectric layer, and forming an antireflective layer on the surface of the metal layer, wherein the antireflective layer is made of titanium nitride TIN. According to the embodiment of the invention, the antireflective layer made of TIN is formed on the surface of the metal layer, the antireflective layer has the characteristics of uniform and dense texture, smooth surface, good elasticity and good adhesion, and the antireflective layer not only can eliminate reflection from the surface of the metal layer, but also can effectively avoid the problem that open circuit or short circuit is caused during electro-migration in the metal layer as holes are formed in some parts of the metal layer due to stress release or hillocks are formed due to accumulation of metal atoms, so as to improve the product reliability.