The present disclosure provides a method for preparing a self-floating transparent nano ultrathin film. According to the present disclosure, the MXene film layer and the nano ultrathin film layer are sequentially subjected to suction filtration on the substrate material by utilizing a vacuum suction filtration technology, and thus a double-film structure is loaded on the substrate material; then an oxidant is subjected to oxidizing and bubbling on the MXene film layer in a permeation way, and thus the substrate material and the nano ultrathin film layer can be separated in a physical isolating manner. Finally, the nano ultrathin film is completely separated in a liquid phase floating separation manner. The nano ultrathin film prepared by the method provided by the present disclosure has a specific thickness and light transmittance through different loading capacities, and the substrate material can be repeatedly utilized.