An auto gain controller (AGC) and a control method thereof are provided. An input signal is amplified by a radio frequency (RF) amplifier and an intermediate frequency (IF) amplifier. When strength of the input signal is lower than a threshold, a gain curve of the RF amplifier is lowered while a gain curve of the IF amplifier is raised. When the strength of the input signal is greater than the threshold, a takeover point (TOP) of the IF amplifier is changed from a first takeover point to a second takeover point.