In conclusion, we collected SAED patterns from different orientations to fit the lattice parameters, demonstrating R-3 space group for α-RuI₃. Density functional theory calculations were employed to discuss the energy advantage of 3R and 2H phases under various pressures, with the former showing lower energy than the latter under the synthesized pressure. Moreover, the ΔH-P curves imply that the 2H phase will emerge at approximately 11 GPa. Furthermore, the in-situ pressure-dependent resistance measurements reveal the metallic behaviour up to 25.5 GPa. Upon cooling from room temperature, the resistance increases first slowly and then rapidly at low pressure. Above 11.9 GPa, the resistance behaviour undergoes a great change—it initially increases fast and then slightly almost independent of temperature. The calculated electronic structure under HP shows semi-metallic behaviour, consistent with the experimental observation. Furthermore, the pressure point, where resistance behaviour dramatically changes, is close to the calculated one when P-31c structure emerges, indicating that the resistance changes may be driven by pressure-induced structure transformation. Our work clarifies the detailed structure of α-RuI₃ and gives an in-depth investigation of its electrical transport behaviour under HP.