The invention provides a power amplifier adaptive to a power supply voltage. The power amplifier comprises a voltage comparison module, which is used for comparing a first power supply voltage with each reference voltage in a plurality of reference voltages, and obtaining a plurality of comparison results; a current setting module, which is used for determining an output current value according to the plurality of comparison results; a linear transconductance circuit module, which is used for determining a grid voltage value of an output stage module according to the output current value; and the output stage module, which is used for outputting a corresponding static working current value according to the grid voltage value. The voltage comparison module can obtain different comparison results according to different values of the power supply voltages, so that the current setting module can determine diffident output current values, and finally, the linear transconductance circuit module can determine different grid voltages of an output stage according to different current values, so that the output stage can output different static working current values, and the range of the power supply voltage of the power amplifier can be effectively expanded.