Provided are an array substrate and a method for manufacturing the same, a display device and a method for manufacturing the same. In the array substrate, the drain of the thin film transistor is extended to form a drain extension line, wherein the drain extension line is between adjacent sub-pixel units of the pixel region, thus it can block the light at the boundary between the sub-pixel units, thereby avoiding light leakage duo to the disordered electric field at the boundary between the sub-pixel units. The array substrate of the present disclosure is suitable for a multi-domain oriented IPS mode array substrate. The drain extension line can be used as a light blocking strip to prevent light leakage due to the disordered electric field at the boundary between the sub-pixels, and is overlapped with the middle portion of the common electrode line to form a storage capacitor.