The invention discloses a substrate, a preparation method thereof and an organic light emitting diode display device. The substrate comprises a metal foil; a metal material for making the metal foil can be subjected to anodizing; and a plurality of recessed light-trapping microstructures are formed on the surface of the metal foil. The modal loss of the substrate due to the total reflection of thesubstrate can be decreased, and the light extraction efficiency of a light emitting device using the substrate can be improved, and a light utilization rate can be improved.