Summary: Metal halide perovskite nanomaterials (PeNMs) are among the next generation of optoelectronic materials due to their unique crystal structure and diverse phase change behaviors, which have the potential to dynamically tune the device performances. In this review, the research progress on the phase change of PeNMs is comprehensively reviewed and summarized. First, the basic structure and composition, as well as the phase change mechanism are introduced. Then, the influence of the phase change on the optoelectronic properties of PeNMs is discussed in detail, including the regulation of the energy band structure, carrier transport properties, lattice strain and distortion, and the evolution of the photoexcited state. Finally, current challenges and future development trends are projected. This review promotes the understanding of the phase change of PeNMs, which will be useful for the innovative design and application of related optoelectronic devices.