All-inorganic　metal　halide　nanocrystals　(NCs)　with　high-efficiency　narrow-band　photoluminescence　(PL)　are　highly　desirable　for　display　applications.　Herein,　we　report　a　strategy　to　achieve　efficient　narrow-band　blue　PL　in　0D　Cs2ZnBr4　NCs　via　minor　Pb2+　doping.　Upon　doping　with　0.1　mol%　Pb2+,　the　intrinsically　non-luminescent　Cs2ZnBr4　NCs　become　efficiently　luminescent,　with　a　sharp　emission　peak　at　433　nm　(full-width　at　half　maximum　of　approximate　to　10.2　nm)　and　a　high　quantum　yield　of　82.9　%.　With　the　aid　of　the　first-principles　calculations,　we　unveil　that　the　narrow-band　blue　PL　originates　from　the　localized　exciton　emission　arising　from　the　peculiar　electronic　band　structure　induced　by　Pb2+　doping,　in　which　the　photogenerated　excitons　in　[PbBr4](2-)　tetrahedra　are　trapped　and　localized　within　[ZnBr4](2-)　tetrahedra.　Furthermore,　by　control　of　the　Pb2+　concentration　(0.1-3.0　mol%),　we　achieve　dual-band-tunable　blue/green　PL　in　Cs2ZnBr4:　Pb2+/CsPbBr3　hybrid　NCs　with　high　efficiency　and　signifcantly　improved　stability　compared　to　that　of　bare　CsPbBr3.　These　findings　provide　a　unique　approach　to　achieve　highly　efficient　narrow-band　PL　in　metal　halide　NCs　via　minor　Pb2+　doping,　which　largely　mitigates　the　toxicity　concern　about　lead　halide　perovskites　and　thus　may　open　up　new　opportunities　for　the　materials　design　and　device　engineering　in　practical　applications.