An OLED substrate, comprising a plurality of light-emitting sub pixels and pixel separation walls; at least one of a hole injection layer, a hole transport layer and an organic light-emitting layer corresponding to at least two light-emitting sub pixels has a different layer thickness; and the upper surfaces of the hole injection layer, hole transport layer and organic light-emitting layer of any light-emitting sub pixel are flush with the upper surface of a hydrophilic film layer of the pixel separation wall. The OLED substrate is used to improve the surface smoothness of each organic layer of a light-emitting sub pixel. Also provided is a display device.