The present disclosure provides an OLED substrate, a manufacturing method thereof, and a display device. The OLED substrate comprises: a base substrate; a source-drain metal extending portion arranged on the base substrate; a passivation layer having via holes at positions corresponding to cathode contact regions in a peripheral area; an anode metal extending portion being electrically connected with the source-drain metal extending portion through the via holes; a pixel definition layer having first patterns at positions corresponding to a display area, each having a protrusion portion and a groove portion; the pixel definition layer having second patterns at positions corresponding to the cathode contact regions, each having a protrusion portion and a groove portion. The protrusion portion of the first pattern corresponds to the groove portion of the second pattern, and the groove portion of the first pattern corresponds to the protrusion portion of the second pattern.