Piezoceramics　with　high　piezoelectric　performance　in　a　wide　elevated　temperature　range　are　the　best　potential　stocks　used　in　advanced　high-temperature　piezoelectric　devices.　Here,　novel　ternary　perovskite　piezoceramics　of　(0.997-x)BiScO3-xPbTiO3-0.003Bi(Zn2/3Nb1/3)O3　(BS-xPT-BZN)　are　synthesized　and　investigated.　The　morphotropic　phase　boundary　(MPB)　composition　of　the　BS-xPT-BZN　system　is　located　at　x　=　0.625,　which　exhibits　a　high　Curie　temperature　(TC)　of　442　degrees　C.　More　excitingly,　the　in-situ　piezoelectric　coefficient　(d33)　of　the　x　=　0.625　MPB　sample　is　not　only　as　high　as　558　pC/N　at　200　degrees　C,　but　also　has　a　fluctuation　rate　of　less　than　&　PLUSMN;　10　%　in　the　ultra-wide　high-temperature　range　of　100　-　308　degrees　C.　The　above　excellent　comprehensive　high-temperature　piezoelectric　performance　should　be　attributed　to　the　synergistic　effect　of　composition-related　MPB　and　dispersion　characteristics　and　thermally　stable　ferroelectric　domain　state.　The　results　demonstrate　that　BS-xPTBZN　ceramics　can　be　used　as　very　competitive　perovskite　piezoelectrics　to　construct　piezoelectric　devices　for　applications　in　harsh　high-temperature　environments.