In this study， I^- doped Cs₃Bi₂Br₉ crystals （Cs₃Bi₂I _x Br_9-x ） were successfully grown using the solution cooling method. The influence of I^- doping on the crystal structure， thermal stability， and optical properties of Cs₃Bi₂Br₉ was systematically investigated. The Cs₃Bi₂I _x Br_9-x crystals obtained through growth have a size of 5 mm.The doped crystal exhibits an orange-red color， which is distinctly different from the yellow color of the undoped crystal. The XRD results show that the doped crystal still maintains a hexagonal structure with the P3m1 space group， while displaying a shift of diffraction peaks towards smaller angles， indicating lattice expansion due to the difference in radius between the I^- and Br^-. Thermal analysis shows that the crystal remains stable up to 475.2 ℃， slightly higher than that of Cs₃Bi₂Br₉. Optical tests reveal that after doping， the crystal absorption cut-off edge redshift from 486 nm to 590 nm， resulting in a decrease in the bandgap from 2.61 eV to 2.18 eV， thus significantly broadening the photoresponse range. The main photoluminescence （PL） peak blue shifts to 447 nm （with a full width at half maximum of 97.7 nm， CIE coordinates （0.27， 0.24））， and the fluorescence lifetime exhibits a double exponential decay （τ₁=2.18 ns， 38%； τ₂=32.32 ns， 62%）. This study confirms that I^- doping can achieve an optimization of the thermal stability and optoelectronic properties of Cs₃Bi₂Br₉ crystals， providing a new pathway for the application of lead-free perovskites in the field of optoelectronic devices.