The invention relates to an electrode assembly based on a flexible substrate, a lithium-oxygen thin film battery, and a preparation method of the electrode assembly. The electrode assembly comprises aflexible substrate, a positive electrode film layer, a negative electrode film layer and a protection layer, wherein the positive electrode film layer and the negative electrode film layer are positioned on the same surface of the flexible substrate, and are separated a certain distance, and the protection layer is positioned on the upper surface of the negative electrode film layer. According tothe present invention, the electrode assembly can be subjected to folding and other flexible treatments; the preparation method is simple and rapid; and the lithium-oxygen thin film battery preparedby using the electrode assembly can achieve the integrated design, the lithium-oxygen battery with characteristics of large capacity and high volumetric specific energy can be conveniently produced, and the high practical value is provided.