The present invention relates to a power transformer noise active control system. The noise of the power transformer is collected to form primary sound source; a signal analyzer is employed for analysis, and after the related analysis is performed, the related conversion is performed; a controller TMS320F28335 is employed to control a related convertor, the convertor controls the sound wave emitted by a secondary loudspeaker to allow the sound wave to offset the noise of a mute area at the position where is 3m far away from a primary sound source center; and a sound pressure sensor is putted at the assigned position of the mute area, when it is detected that the sound pressure at the position is changed, the newest sound pressure value is sent to an intelligent controller, and the intelligent controller timely makes up analysis according to the input and output conditions of the system at the moment and regulates the secondary sound source amplitude and phase position so as to reduce the noise of the assigned position of the mute area.