The embodiments of the present invention provide a substrate and a manufacturing method thereof, as well as a display device. The substrate comprises: a base substrate, a plurality of gate lines arranged in parallel, a first insulating layer that covers the gate lines, a plurality of data lines located on the first insulating layer and perpendicular to the gate lines, a second insulating layer that covers the data lines, and pixel electrodes of sub-pixel areas enclosed by the data lines and the gate lines; polarizing films that cover the pixel electrodes; and first auxiliary gate lines arranged on the second insulating layer and parallel to the gate lines, at least two portions on each of the first auxiliary gate lines being electrically connected with at least two corresponding portions on the gate line through via holes that penetrate the first insulating layer and the second insulating layer, the first auxiliary gate lines and the polarizing films are formed by performing a same patterning process to a same layer of transparent conductive material. The embodiments of the present invention can reduce signal delay in a display device, and can be used for manufacture of a display.