A supporting plate and a foldable display device are provided. The supporting plate includes at least one bending region and non-bending regions. The bending region includes two semi-bending regions bent symmetrically along a bending axis. Any of the semi-bending regions includes an internally bending region and an externally bending region. The internally bending region is located on an end away from the non-bending regions. The externally bending region is located on an end close to the non-bending regions and has a bending direction opposite to the internally bending region. The semi-bending regions include a plurality of openings spaced apart. A distribution density of the openings in the internally bending region is greater than a distribution density of the openings in the externally bending region.