Abstract: A system for controlling fan noise includes a fin, a fan, a sensor, a signal processing unit, and a speaker. The fin has a front side and a rear side opposite to the front side. The fan is disposed adjacent to the front side and has an airflow outlet, and the airflow outlet faces the front side. The sensor is disposed adjacent to the rear side and is used for receiving a sound signal made by the fan. After the signal processing unit receives the sound signal sent by the sensor, the signal processing unit provides an inversed phase signal by analysis and computation. The speaker is disposed adjacent to the rear side, for receiving and outputting the inversed phase signal provided by the signal processing unit, so as to offset the noise made by the fan.