A method of fabricating a substrate includes forming a planarization layer, and forming the planarization layer includes: forming a first planarization sub-layer on a base substrate on which a patterned film layer has been formed. A surface of the first planarization sub-layer facing away from the base substrate has a plurality of depressed portions. Forming the planarization layer further includes: forming a second planarization sub-layer at multiple depressed portions of the plurality of the depressed portions to obtain the planarization layer including the first planarization sub-layer and the second planarization sub-layer. A flatness of a surface of the planarization layer is higher than a flatness of the surface of the first planarization sub-layer.