As a promising new material， metal halide perovskite is rising as a shining star in the field of optoelectronics. In this paper， 3D CsPbBr₃ perovskite nanocrystals were prepared by a conventional thermal injection method. The phase transitions between 3D CsPbBr₃， 0D Cs₄PbBr₆， and 2D CsPb₂Br₅ have been realized by adding ligands or polar solvents， and their unique optical properties were investigated and compared. Under UV excitation， CsPbBr₃， CsPbBr₃@Cs₄PbBr₆， and CsPbBr₃@CsPb₂Br₅ all emit bright green light with fluorescence lifetime on the nanosecond scale. The fluorescence lifetime of the composite structures CsPbBr₃@Cs₄PbBr₆ and CsPbBr₃@CsPb₂Br₅ is almost the same as that of CsPbBr₃， suggesting that the emission of the CsPbBr₃@Cs₄PbBr₆ and CsPbBr₃@CsPb₂Br₅ complexes are all from CsPbBr₃ nanocrystals. In addition， the addition of ligands enabled the transformation of CsPbBr₃ to Cs₄PbBr₆， and the polar solvent water-induced phase transition from CsPbBr₃ to CsPb₂Br₅ was also confirmed. This work not only provides a simple method for the preparation of composite structured perovskites， but also provides some knowledge about the degradation of lead-halide perovskites in humidity environment.

perovskites;dimension;optical properties;phase transition