An OLED display substrate, a manufacturing method thereof, and a display device are provided. The OLED display substrate includes a base substrate, a conductive pattern, a driving circuit layer, an anode layer, a light-emitting layer and a cathode layer. The driving circuit layer, the anode layer, the cathode layer and the light-emitting layer are arranged at a same side of the base substrate. The conductive pattern is arranged between the base substrate and the driving circuit layer and electrically connected to the cathode layer through a plurality of via holes.