The invention relates to the field of power amplifiers. A power amplifier provided by an embodiment of the invention comprises (n+1) amplifying units in parallel coupled connection, wherein n is an integer greater than or equal to 0; third input ends VR (i) of the (n+1) amplifying units are in coupled connection with a power input VL; the output ends D (i) of the (n+1) amplifying units are in coupled connection with a power input VH; the output power of the power amplifier is in an increasing function relationship with a capacitance value obtained by accumulating the return energy capacitancexC of the (n+1) amplifying units. The power amplifier provided by the embodiment of the invention changes the circuit impedance by controlling the shunt capacitance value through a switch digital signal, so as to control the magnitude of the return power value and form different output power. The invention effectively solves the problem of power loss and low efficiency caused by the traditional power amplifier.