A portable electronic device and method executes control functions by variations of a light intensity. The portable electronic device comprises a memory, a touch screen, a proximity sensor and at least one processor. The light sensor detects an original light intensity and a current light intensity surrounding the portable electronic device when the touch screen is turned on. If a difference in light intensity between the original light intensity and the current light intensity is more than a predetermined value, the portable electronic device controls a user interface displayed in the touch screen accordingly.