The present invention provides a device and method for controlling screen brightness. The method comprises: a light sensor acquiring a brightness signal intensity value of external environment and transmitting the brightness signal intensity value to a comparator; the comparator comparing the received brightness signal intensity value with a stored brightness signal intensity value and outputting a comparison result to an integrator; if the comparison result is that the received brightness signal intensity value is greater than the stored brightness signal intensity value, the integrator increasing the stored brightness signal intensity value by a fixed value according to the comparison result; and if the comparison result is that the received brightness signal intensity value is less than the stored brightness signal intensity value, the integrator decreasing the stored brightness signal intensity value by a fixed value according to the comparison result.