The present invention discloses a phase adjustment apparatus. The phase adjustment apparatus includes at least two phase adjustment units, a switching apparatus, and a driving apparatus; where the at least two phase adjustment units are configured to modulate a phase; the driving apparatus is configured to drive the at least two phase adjustment units to move; the at least two phase adjustment units are selectively connected to the driving apparatus; and the switching apparatus is configured to select the at least two phase adjustment units, so that the driving apparatus drives, at a same moment, only one of the at least two phase adjustment units connected to the driving apparatus to move, so as to change a phase. The present invention discloses a multi-frequency antenna which applies the phase adjustment apparatus. The phase adjustment apparatus of the present invention may adjust a downtilt angle of an antenna unit.