Raman spectra of pyromellitic dianhydride crystal have been measured from ambient to 24 GPa, and the Raman vibrational modes of pyromellitic dianhydride have been assigned. Based on the pressure dependence of Raman mode frequencies, it can be observed that a phase transition of pyromellitic dianhydride occurred from Phase Ⅰ to Phase Ⅱ at 2 GPa. In comparing the slopes of the pressure dependence of the Raman vibrational modes between Phase Ⅰ and Phase Ⅱ, it can be found that most of the slopes of Phase Ⅰ were smaller than Phase Ⅱ. The results indicate that the sensitivity of functional groups of pyromellitic dianhydride to pressure decreases with increasing pressure, and the molecular crystal of pyromellitic dianhydride has a more compact stacking structure in phaseⅡ. Besides, we also calculated the Raman intensities ratio of the overtone of C—O stretching vibration mode (located at 1 837 cm-1) and the fundamental of CO stretching vibration mode (located at 1 865 cm-1) and the discontinuities of the Raman intensities ratio versus pressure was observed. This behavior confirms that the pyromellitic dianhydride crystal has undergone a phase transition at 2 GPa, as mentioned above.