The invention relates to a device for controlling quantizing noise leakage in the technical field of communications, comprising a transient signal detecting unit and an alternative control unit, wherein, the transient signal detecting unit is used for dividing a currently input frame signal into a plurality of subframes, calculating a maximum amplitude value of each subframe and adopting the ratio of the maximum amplitude value of each subframe and the sum of the maximum amplitude values of adjacent subframes of the individual subframe as a transient detection function; the ratio is judged, if the ratio is more than a certain threshold value, then the transient signal is detected, if not, the transient signal is not detected and a transient signal detection result is transmitted; the alternative control unit is used for receiving the transient signal detection result and choosing different branch routes for encoding processing regarding different signals. The invention also provides amethod for controlling quantizing noise leakage and solves the problems in the existing proposal for controlling quantizing noise leakage that the computational complexity is high, the time delay is long, the encoding efficiency is low and the occupied resources are more.