An array substrate and a manufacturing method thereof, a display device and a thin film transistor are provided. The method includes forming a pattern that includes an active layer, a pixel electrode and a data line on a base substrate; forming a pattern that includes a gate insulating layer and at least two gate via-holes therein, the at least two gate via-holes are located in regions in the gate insulating layer that correspond to outer surroundings of the active layer and do not overlap with areas where the pixel electrode and the data line are located; forming a pattern that includes a gate line and at least two gate electrodes, the at least two gate electrodes are connected to the gate line, and are provided in the at least two gate via-holes, respectively. With this method, the fabricating process and the fabricating cost are saved.