A bias circuit for the wireless transceiver is disclosed, which can be used for modulating the gain of the amplifier. The bias circuit comprises a first stage bias unit for receiving a constant current, a control voltage, and a first reference voltage and outputting a first outputting current, wherein the control voltage is used for controlling the value of the first outputting current, and further, the first outputting current can be increased or decreased by representing as an analog form, thus, the gain of the amplifier can be modulated according to the first outputting current, and the modulation of the gain can be represented as an analog form, such that the transient response occurred while the gain is modulated can be reduced.