An array substrate and a manufacturing method thereof and a display device are provided. The manufacturing method includes: forming a first signal line and a second signal line which have a same extension direction and are separated from each other on a base substrate; forming an initial pixel electrode on the base substrate, such that the initial pixel electrode includes a first extension portion, and the initial pixel electrode is connected to the first signal line by the first extension portion and the initial pixel electrode is separated from the second signal line; and removing at least part of the first extension portion of the initial pixel electrode to form the pixel electrode separated from the first signal line.