An array substrate and a manufacturing method thereof, and an OLED display device are provided. The array substrate comprises: sub-pixel units defined by gate lines and data lines that cross with each other on a substrate, each of the sub-pixel units comprising a first TFT, a second TFT and a pixel electrode, a gate electrode of the first TFT being connected to the gate line, a source electrode of the first TFT being connected to the data line, and a drain electrode of the second TFT being connected to the pixel electrode. The source electrode and a drain electrode of the first TFT are formed on the same layer as a gate electrode of the second TFT, and the drain electrode of the first TFT is directly connected to the gate electrode of the second TFT.