The present disclosure provides an organic light emitting display panel and a fabricating method thereof, and a displaying device. The method includes: forming an anode-material layer on a base plate, forming a mask on one side of the anode-material layer that is away from the base plate, and performing patterning treatment to the anode-material layer by using the mask, to form a plurality of anodes; and forming a pixel definition layer covering the mask and the base plate, wherein the pixel definition layer is provided with slots between the plurality of anodes, and performing patterning treatment to the pixel definition layer and the mask at the same time, to form a plurality of pixel defining components, wherein the pixel defining components cover parts of the base plate that are located between two neighboring anodes, and cover part of surfaces of the anodes; and a material forming the mask and a material forming the pixel definition layer are the same, each of the pixel defining components includes a first part formed by the mask, and a second part formed by the pixel definition layer, and the slots are located in the second parts.