A gain control circuit utilized in a transmitter is disclosed. The transmitter is configured to amplify an input signal according to a gain via a digital amplifier, an analog amplifier and a power amplifier, to generate an output signal. The gain control circuit includes a correction unit configured to calculate a correction power according to an elapsed time since a current packet transmission duration of the transmitter is completed. The gain control circuit adjusts the gain according to the correction power, a transmitter signal strength indication of the input signal and an environment temperature of the transmitter.