The present invention provides an apparatus and a method for amplifying a radio-frequency signal and an MRI system comprising the apparatus. An aspect of the present invention proposes an apparatus for amplifying a radio-frequency (RF) signal comprising: a magnetically insensitive input balun (10) for converting the RF signal in unbalanced format into balanced signals; at least two groups of MOSFETs, each group including at least one MOSFET (30, 40), for respectively amplifying the balanced signals in a push-pull way; a magnetically insensitive output balun (60) for converting the amplified balanced signals into an unbalanced format; a magnetically insensitive input matching network (20, 20′) for matching input impedances of the at least two groups of MOSFETs with output impedances of the magnetically insensitive input balun (10); a magnetically insensitive output matching network (50, 50′) for matching output impedances of the at least two groups of MOSFETs with input impedances of the magnetically insensitive output balun (60); a magnetically insensitive protection circuit (70, 70′) for protecting a direct current (DC) power supply which provides DC for driving the at least two groups of MOSFETs from the amplified balanced signals. The proposed apparatus not only has a high power output but is also magnetically insensitive, so that it can operate in an environment of strong magnetic fields, such as the MRI scanner room.