An adjustable gain power amplifier, a gain adjustment method and a mobile terminal are disclosed. The adjustable gain power amplifier comprises an input matching circuit, a gain adjustment circuit, a biasing circuit, a main amplification circuit, and an output matching circuit; the input matching circuit is connected between an input end and the gain adjustment circuit; the gain adjustment circuit is connected between the input matching circuit and the input end of the main amplification circuit; the output end of the main amplification circuit is connected to the output matching circuit, a positive power source end thereof is connected to a power supply source, a negative power source end thereof is connected to the biasing circuit; the biasing circuit provides different biasing voltages for the main amplification circuit; and the gain adjustment circuit and the biasing circuit are respectively connected to a gain adjustment control voltage (Vctrl).