An OLED display substrate and a display device are provided. The OLED display substrate includes a plurality of sub-pixel regions corresponding to different colors arranged on a substrate. Each sub-pixel region includes a thin film transistor, an anode, a light-emitting layer and a cathode arranged successively in a direction away from the substrate, and a microcavity structure is formed between the anode and the cathode. The anode includes a hollowed-out portion, the light-emitting layers of the sub-pixel regions corresponding to different colors are of different thicknesses, or the anodes of the sub-pixel regions corresponding to different colors are of different thicknesses.