An adjustment module, an electronic device with the adjustment module, and an antenna performance adjusting method thereof are disclosed. The adjustment module is used for adjusting an antenna module. The antenna module is disposed in the electronic device and used for radiating a wireless signal. The adjustment module includes a monitoring module, a determining module, and a capacitance adjusting unit. The monitoring module is used for detecting an alternating current signal waveform when the antenna module radiates the wireless signal. The determining module receives the alternating current signal waveform and is used for generating an adjusting voltage value when the alternating current signal waveform is a non-constant amplitude. The capacitance adjusting unit is used for changing a capacitance value according to the adjusting voltage value to adjust a resonance point coordinate of the antenna module.