The present disclosure provides an OLED display panel, a preparation method thereof and an OLED display device. By providing an uneven surface on a side of a first encapsulation layer away from the organic light-emitting function layer in a non-display area, the uneven surface of the first encapsulation layer can block the flow of the second encapsulation layer to a certain extent, so as to reduce the fluidity and the climbing distance of the edge of the second encapsulation layer, and increase the edge stress and the slope angle. Thereby the narrow frame design of the product is achieved, the thickness uniformity of the edge of the second encapsulation layer is improved, the Mura defect in the non-display area is avoided, and the encapsulation result is guaranteed.