Jadeite, the principal mineral constituent of jadeite jade, is widely regarded as the “king of jade”. Under high-pressure conditions, both artificial jadeite-jade synthesis and the modification of natural jadeite jade involve transformations between crystalline jadeite and a glass with the same composition. Therefore, clarifying the onset boundaries of the jadeite-to-glass transformation and the glass-to-jadeite crystallization in the NaAlSi₂O₆ system under high-pressure heating conditions is important for understanding the phase transformation behavior of this system and for optimizing related synthesis and modification processes. In this work, the bidirectional transformation behavior between jadeite and glass in the NaAlSi₂O₆ system was systematically investigated over the pressure range of 0–5 GPa under continuous heating. High-pressure in situ differential thermal analysis was used to determine the thermal anomalies and onset temperatures of the transformations, and the phase and microstructural characteristics of the quenched samples were examined by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results show that the onset temperature of the jadeite-to-glass transformation increases markedly with increasing pressure. It increases from approximately 1116 ℃ at 1.3 GPa to approximately 1750–1850 ℃ at 5.0 GPa, indicating that high pressure significantly enhances the thermal stability of crystalline jadeite. In contrast, no clear crystallization of NaAlSi₂O₆ glass was observed at approximately 2.2 GPa under the present heating path and holding conditions. When the pressure increases to 3.0–5.0 GPa, glass-to-jadeite crystallization occurs, but its onset temperature remains nearly constant at 1000–1050 ℃, showing only weak pressure dependence. This behavior suggests that the crystallization process is more strongly constrained by kinetic factors such as nucleation, crystal growth, and atomic diffusion. The comparison of the two opposite transformation processes reveals a pronounced asymmetric pressure response of the onset boundaries between jadeite and glass in the NaAlSi₂O₆ system. The main contribution of this work is to establish, within a unified experimental framework, the onset boundaries of the jadeite-to-glass and glass-to-jadeite transformations under continuous high-pressure heating, rather than only discussing equilibrium phase relations or individual crystallization conditions. These results provide an experimental reference for understanding the actual transformation behavior of the NaAlSi₂O₆ system under non-equilibrium heating paths and for selecting pressure-temperature windows in high-pressure jadeite synthesis and heat-treatment processes.