The triuranium octoxide (U₃O₈) exhibits exceptional kinetic and thermodynamic stability among various uranium oxides. The study of the high-pressure phase stability and high-pressure phonon behaviour of U₃O₈ is an important reference for its application in the nuclear industry, catalysts, and other fields. Due to the complexity of the electron structure outside the nucleus of the uranium atoms (［Rn］5f³6d¹7s²), compared to the oxygen atoms (［He］2s²2p⁴), significant differences exist between their electron configurations. Therefore, synchrotron X-ray diffraction makes it difficult to detect subtle changes in U—O bonding for uranium oxides under high pressure. However, Raman spectroscopy is highly sensitive to changes in U—O bonding at high pressure, and it can reveal some important information about substances at high pressure, including bonding or stoichiometry. To date, the investigations on the high-pressure structural phase transition for U₃O₈ have typically focused on exploring its evolution in hydrostatic environments. However, a deep investigation of the effects of non-hydrostatic environments on the high-pressure phase transition of U₃O₈ has not been conducted yet. In this work, the effects of hydrostatic and non-hydrostatic environments on the high-pressure phase transition and phonon behaviour for orthorhombic α-U₃O₈ have been investigated using a high-pressure Raman scattering technique based on the diamond anvil cell. Our results show that initialization transition pressures of α-U₃O₈ under hydrostatic (8.1 GPa) and non-hydrostatic (8.2 GPa) conditions are very close. However, the significant micro zonation bias stress present within the sample in the non-hydrostatic environments leads to the completion transition pressure (16.4 GPa) being approximately 2 to 3 GPa lower compared to the corresponding values in the hydrostatic environments (18.5 GPa). The first-order pressure coefficients and mode-Grüneisen parameters γ of the main Raman modes in two comparison experiments were given. The results show that before the high-pressure phase transition, the absolute values of the zero-pressure first-order pressure coefficients |dω/dP| for the main Raman modes under the hydrostatic environments are generally greater than those under the non-hydrostatic environments, which indicates that the Raman modes exhibit an insignificant response to the pressure under the non-hydrostatic environments. However, the absolute values of the first-order pressure coefficients under the non-hydrostatic environments are significantly larger once the high-pressure phase transition begins. This may be caused by significant micro zonation bias stress that greatly strengthens the mutual coupling between the outer electrons of the uranium-oxygen atoms. The $$B_2^{（6）}$$ mode exhibits the smallest γ value at zero pressure, indicating a more positive response to external perturbations. Moreover, the first-order pressure coefficients of the $A_2^{(3)}$ and $$A_2^{(4)}$$ modes (representing the vibrations of the oxygen atoms along the a-axis) are typically smaller than those of the $B_2^{(4)}$ and $$B_2^{（6）}$$ modes (representing the displacements of the oxygen atoms in the bc-plane) when pressurized at room temperature, suggesting that the a-axis is less sensitive to pressure than the b-axis and c-axis before the high-pressure phase transition for α-U₃O₈. The effect of hydrostatic and non-hydrostatic environments on the high-pressure phase transition for α-U₃O₈ was investigated deeply for the first time in this work, which offered valuable insights into the high-pressure phase stability and lattice dynamics behavior of α-U₃O₈.