Abstract: An automatic gain control method used in a wireless receiver is disclosed. The method comprise the following steps: Receiving a first frame, amplifying a RF signal corresponding to the first frame with a gain value and down converting the RF signal to generate a baseband signal. Updating the gain value according to the power level of the baseband signal corresponding to the first frame, then using the updated gain value to amplify the RF signal corresponding to a second frame when receiving the second frame. Determining whether a first signal block is in the discontinuous transmission mode or not, wherein the first frame belongs to the first signal block. And resuming the gain value according to the power level of the baseband signal corresponding to a third frame if the first signal block is in the discontinuous transmission mode.