Transparent　ferroelectrics　with　high　piezoelectricity　are　highly　desirable　for　acousto-optic-electrical　multifunctional　coupling　devices.　However,　it　is　challenging　to　simultaneously　achieve　high　piezoelectricity　and　perfect　transparency　in　lead-free　piezoelectric　ceramics　because　of　the　contradiction　between　the　inherent　characteristics　of　traditional　high　piezoelectricity　and　the　transparency.　Here,　we　demonstrate　an　efficient　method　to　tailoring　the　microstructure　in　originally　poor　piezoelectricity　fine-grain　KNN-BNN　ceramics　to　simultaneously　exhibit　excellent　transparency,　an　superior　piezoelectric　coefficient　(similar　to　185　pC/N,　highest　in　KNN-based　transparent　ceramics),　an　excellent　EO　coefficient　(similar　to　84　pm/V),　and　high　T-c　(similar　to　350　degrees　C).　Combining　the　multiple　in-situ　characterizations　and　DFT　simulations,　we　found　that　both　the　piezoelectricity　and　EO　effect　of　fine-grain　KNN　transparent　ceramics　can　be　greatly　improved　without　greatly　reducing　the　transparency　via　tailoring　the　structure　of　phase　and　domains　to　enhance　local　inhomogeneity,　enabling　prominent　acousto-optic-electrical　multifunctional　coupling　in　vivid　potential　applications,　such　as　self-energy-harvesting　touch　screens,　invisible　robotic　devices　and　electro-optic　(EO)　devices.　(C)　2022　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.