A method for preparing a flexible display device comprises: forming a release layer (2) on a transparent hard substrate (1), the release layer (2) being made of an ultraviolet light decomposition material to which an inert substance is added; integrating a flexible substrate (4) onto the transparent hard substrate (1) having the release layer (2), the flexible substrate (4) being opposite to a side having the release layer (2) of the transparent hard substrate (1); forming a display component (5) on the flexible substrate (4); and exposing a side far away from the release layer (2) of the transparent hard substrate (1) to ultraviolet rays (7), so as to trigger the release layer (2) to undergo a photochemical reaction with gas releasing, so that the transparent hard substrate (1) is separated from the flexible substrate (4). The method for preparing a flexible display device can simplify a process of producing a flexible display device.