The invention discloses a flexible display device and a preparation method thereof. The method comprises that an inorganic sacrificial layer, a flexible substrate and a display screen are prepared ona rigid substrate successively, and a bonding force between the flexible substrate and the inorganic sacrificial layer is lower than that between the inorganic sacrificial layer and the rigid substrate; laser is used to cut the flexible substrate, the edge of the flexible substrate after cutting is separated from the inorganic sacrificial layer due to contraction caused by laser burning, and a laser cutting position is between the edge of the display screen and the edge of the flexible substrate; and the flexible substrate is peeled from the rigid substrate along the contracted position of theedge of the flexible substrate via a mechanical outside force. Via the method, the whole flexible substrate is avoided from influence of high temperature caused by laser, the display screen is not damaged, and the service life of the flexible display device is not influenced.