Pb_0.9625Sm_0.025[(Mg_1/3Nb_2/3)_0.71Ti_0.29]O₃ ceramic material with a high piezoelectricity wasprepared by a two-step oxide solid reaction method. The effects of driving field amplitude and temperature on the radial resonance characteristics were investigatedby a large signal resonant response test system. The results show that the resonant response at a low driving field can maintain a single resonant peak until complete depolarization. However, the resonant response becomes complicated, and some multiple resonant peaks appear even at a low temperatureas a driving field increases. The resonant properties areclosely related to the mechanical quality factor Q_m, ferroelectric domain size and phase composition. The thermal effect produced by applying a high driving field on the low Q_m material accelerates the splitting of macro-domains and induces a first-order ferroelectric phase transition. The instability of resonant characteristics and the large resonant frequency temperature coefficient restrictthe application of Sm-doped PMN-PTrelaxor ferroelectric ceramics, especially at a high driving field.