A substrate and a manufacturing method thereof and a display device are provided. The substrate includes: a base including a bendable region; an interlayer on the base and in the bendable region; and a signal line at a side, facing away from the base, of the interlayer. In the bendable region, an orthographic projection of the signal line on the base is within an orthographic projection of the interlayer on the base; and in the bendable region, the interlayer is provided with a groove on at least one side of a portion, corresponding to the signal line, of the interlayer.