The present disclosure discloses a thin film transistor array substrate including an active layer disposed on a base substrate, wherein the active layer includes a first active region and a second active region located in a same structural layer, the first active region has a material comprising poly-silicon, and includes a first channel region, and a first source region and a first drain region that are located at both sides of the first channel region, respectively, the first source region having a first contact layer disposed thereon, the first drain region having a second contact layer disposed thereon, and materials of both the first and second contact layers being boron-doped poly-silicon; and the second active region has a material comprising metal oxide semiconductor, and includes a second channel region and a second source region and a second drain region that are located at both sides of the second channel region, respectively. The present disclosure also discloses a preparing method for the thin film transistor array substrate as mentioned above, and an OLED display device including the array substrate.