A magnetic resonance imaging (MRI) system radio frequency (RF) subsystem and a coil decoupling apparatus and method used therein. The MRI system RF subsystem comprises a body coil and a surface coil for receiving MR signals, and also comprises a preamplifier for amplifying the MR signals received by the body coil; the coil decoupling apparatus comprises a phase shifter, which is connected between the preamplifier and the body coil, and used for receiving an external voltage regulation signal to regulate an operation voltage thereof, wherein the voltage regulation signal is determined according to a current patient's weight.