<p>This work presents a visual growth strategy based on water-induced phase transitions, which enables real-time tracking and structural regulation of Cs₄PbBr₆-to-CsPbBr₃ microcrystal transformation under ambient conditions without the need for high-energy beams or vacuum. Driven by the difference in the dissolution rates of CsBr and PbBr₂ in water, the slow progression of the reaction interface allows clear observation of crystal morphology evolution under a conventional fluorescence microscope. The microcrystals obtained through strategy possess highly regular structural morphology and superior optical properties. In the experiments, micron-scale-wire exhibiting size-dependent polarized emission and bulk-microcrystals supporting multimode lasing emission were successfully constructed. Further analysis revealed the significant influence of crystal size on excited-state dynamics, cavity mode selectivity, and emission characteristics, thereby establishing a direct link between structural visual regulation and functional photon output. This work delivers mechanistic insights and experimental evidence for controllable fabrication of low-threshold lasers and polarized light-emitting devices.</p>