The embodiments of the invention provide a display device, a thin film transistor, an array substrate and a manufacturing method thereof. The manufacturing method comprises: step A, forming patterns of a source electrode, a drain electrode, a data line and a pixel electrode; step B, forming an active layer and agate insulating layer in order, and forming a via hole in the gate insulating layer for connecting the data line and an external circuit; and step C, forming patterns of a gate electrode, a gate line and a common electrode line, or forming a pattern of a gate electrode, a gate line and a common electrode.