An embodiment of the invention provides a calibration control method performed by a microphone system. The microphone system includes a plurality of microphones configured to generate a plurality of microphone signals. First, the microphone system equalize the microphone signals to generate a plurality of equalized microphone signals. Next, the microphone system calculates a set of similarity indicators based on the equalized microphone signals. Then, the microphone system compares the set of similarity indicators with a set of predetermined thresholds to determine whether to calibrate the microphone signals.