A flexible display device and a method for changing shape of the flexible display device are provided. The flexible display device includes a flexible display panel and a shape memory structure on the flexible display panel and including a shape memory component. The shape memory component includes a first memory layer, a first thermal insulation layer and a second memory layer stacked sequentially in a direction away from the flexible display panel, the first and second memory layers each have shape memory function, the first memory layer has a first memory shape and the second memory layer has a second memory shape different from the first memory shape. The shape memory structure is configured to switch shape of the shape memory component between the first and second memory shapes by controlling temperatures of the first and second memory layers, thereby driving the flexible display panel to change shape.