A portable electronic device includes a main body, a slidable cover, a display panel, a sensor, and a controlling module. The slidable cover is slidably positioned on the main body. The display panel is positioned on the slidable cover. The sensor is configured to detect a position of the slidable cover relative to the main body. The controlling module is configured to output icons and data to the display panel, and to adjust an area of each icon displayed on the display panel according to a position, detected by the sensor, of the slidable cover relative to the main body.