An amplifier device includes an amplifying unit, a bias module, an impedance unit and an adjusting module. The amplifying unit has a first end coupled to a voltage source and used for outputting an output signal amplified by the amplifying unit, a second end used for receiving an input signal, and a third end coupled to a first reference potential terminal. The bias module is coupled to the second end of the amplifying unit, and provides a bias voltage to the amplifying unit and adjusts linearity of the amplifier device according to a source voltage from the voltage source. The impedance unit is coupled to the bias module and used to receive a control voltage to adjust an impedance value of the impedance unit. The adjusting module is used to output the control voltage to the impedance unit according to the source voltage and a reference voltage.