Abstract: High-pressure-induced structural phase transitions constitute a crucial pathway for discovering new phases and understanding material behaviors under extreme conditions. However, the transition pathways, intermediate states, and dynamics have long remained in a "black box", necessitation in situ probing techniques for elucidation. This article reviews the recent progress in in situ probing techniques and mechanistic studies of structural phase transitions in high-pressure solid-state chemistry. First, the principles and applicable scopes of in situ characterization methods are introduced according to information levels, including X-ray diffraction, neutron diffraction, X-ray absorption fine structure, pair distribution function, Raman spectroscopy, infrared spectroscopy, ultraviolet-visible absorption, fluorescence, and second harmonic generation. Emerging directions such as ultrafast time-resolved techniques and machine-learning-assisted data analysis are also discussed. Second, using displacive phase transitions (SrTiO3), reconstructive phase transitions (graphite-diamond, Co3P2O8), pressure-induced amorphization (ice), isostructural phase transitions (Ce), and order-disorder phase transitions (IMMHyPbBr4) as representative examples, we demonstrate how in situ techniques reveal the microscopic mechanisms of pressure-driven structural evolution. Finally, current bottlenecks in time resolution and data interpretation are summarized, and future directions including multi-technique integration, ultrafast probing, and machine learning are prospected.

Key words: Pressure-induced phase transition, In-situ characterization, Diamond anvil cell（DAC）, Synchrotron radiation