A　combination　of　transparency　and　photochromic　(PC)　properties　in　ferroelectrics　has　promising　application　potential　in　smart　windows　and　optical　storage/imaging.　Nonetheless,　limited　by　understanding　the　underlying　PC　mechanism,　a　splendid　PC　performance　is　rarely　achieved　in　transparent　ferroelectrics.　Here,　a　strategy　to　construct　deep-lying　traps　by　ion-doping　induced　defect　engineering　in　(K0.5Na0.5)-　NbO3-based　ferroelectric　ceramics　is　proposed.　Based　on　the　improved　density　functional　theory　simulations,　a　high　concentration　of　vacancy　defects　can　be　realized　by　codoping　1　mol　%　Pr　and　4　mol　%　Ba　in　(K0.5Na0.5)NbO3,　which　helps　achieving　deep-lying　traps　and　then　superior　PC　performance.　Through　traditional　pressureless　sintering,　highly　transparent　ceramics　with　designed　optimal　composition　have　been　fabricated　in　a　wide　sintering　temperature　range　(1170-1210　degrees　C),　exhibiting　an　ultrafast　PC　feature,　i.e.,　0.1　s　response　time　(by　illumination　of　400　nm　light),　along　with　high　PC　efficiency　(5.8　cm2　center　dot　W-1)　and　PC　rate　(7.1　s-1),　preeminent　among　reported　inorganic　PC　transparent　materials.　Additionally,　the　ceramics　have　been　utilized　for　real-time　optical　recording,　displaying　unambiguous　patterning　with　long-time　preservation　(21　days).　This　research　supplies　a　paradigm　for　designing　high-performance　PC　transparent　materials　in　optical　applications　and　helps　deepen　the　comprehensive　understanding　of　the　PC　mechanism.