The　temporal　evolution　of　domain　structure　and　its　piezoelectric　behavior　of　ferroelectric　material　BaTiO3　during　the　transition　process　from　rhombohedral　to　tetragonal　phase　under　an　applied　electric　field　have　been　studied　by　employing　Landau-Ginzburg　theory　and　the　phase-field　method.　The　results　obtained　show　that,　during　the　transformation　process,　the　intermediate　phase　was　monoclinic　MA　phase,　and　several　peak　values　of　piezoelectric　coefficient　appeared　at　the　stage　where　obvious　change　of　domain　pattern　occurred.　In　addition,　by　comparing　the　cases　of　applied　electric　field　with　different　frequencies,　it　was　found　that　the　maximum　piezoelectric　coefficient　obtained　decreased　with　increasing　frequency　value.　These　results　are　of　great　significance　in　tuning　the　properties　of　engineering　domains　in　ferroelectrics,　and　could　provide　more　fundamentals　to　the　design　of　ferroelectric　devices.