The present disclosure provides a mask plate, an OLED display substrate and a method for manufacturing the OLED display substrate, and a display device. The mask plate comprises a plurality of openings arranged as an array and configured to prepare patterns of a pixel definition layer, wherein a width of the opening close to a first side of the mask plate in a first direction is greater than that of the opening away from the first side of the mask plate, and the first direction is a direction from the opening close to the first side of the mask plate to the opening away from the first side of the mask plate. A slope angle of the pattern of the pixel definition layer close to a second side of the OLED display substrate is smaller than that away from the second side of the OLED display substrate.