The present invention discloses a backlight system and a display device. In the backlight system, corresponding at least one beam expanding plate is arranged at the emergent side of a backlight module, and include a horizontal beam expanding plate and/or a vertical beam expanding plate, wherein each beam expanding plate includes an upper beam expanding sub-plate and a lower beam expanding sub-plate having the same periodic curved surface structures, the upper beam expanding sub-plate and the lower beam expanding sub-plate are arranged in parallel in such a manner that periodic curved surface structures are back-to-back against each other, and the relative position of the upper beam expanding sub-plate and the lower beam expanding sub-plate in the horizontal direction can be adjusted parallelly within a set range.