An array substrate and a manufacturing method thereof, a display panel and a display device are provided. The array substrate manufacturing method comprises: forming a source electrode and a drain electrode on a gate insulating layer; forming photoresist above the gate insulating layer and the source electrode and the drain electrode; etching the photoresist to form an opening region so as to expose the gate insulating layer between the source electrode and the drain electrode, and a part of the source electrode and a part of the drain electrode; and forming an active layer in the opening region, the active layer covering the exposed gate insulating layer, the part of the source electrode and the part of the drain electrode.