A shrouded impeller is an essential component of a liquid rocket, mainly responsible for transporting and pressurizing liquid fuel or oxidant. Owing to the low temperature and high-rotation speed of the working environment, materials with high performance are required for fabricating the impeller. With its excellent low temperature mechanical properties and high specific strength, Ti-5Al-2.5Sn extra-low interstitial (ELI) alloy has been widely applied in fabricating liquid rocket components, including the shrouded impeller. Considering the geometric complexity of the impeller, the powder metallurgy-hot isostatic pressing (PM-HIP) route is a suitable method for impeller formation. PM-HIP technology has a similar forming capability as precision casting but avoids casting defects, realizing the parts with reliable service performance. However, the mechanical properties and dimensional accuracy of the impeller may be influenced by the variation of powder particle sizes. Herein, three kinds of Ti-5Al-2.5Sn ELI prealloyed powders with different particle size distributions (average particle size D₅₀ = 125, 94, and 73 μm) were prepared by adjusting the process parameters of gas atomization and screen meshes. Then, their corresponding shrouded impellers were manufactured via the PM-HIP route at 940 ^oC, 120 MPa for 3 h. Subsequently, the impellers were annealed at 815 ^oC for 1.5 h, followed by air cooling. The effect of powder particle sizes on the mechanical properties of shrouded impellers was analyzed using cryogenic-temperature tensile tests. The porosity defect of impeller slices was detected using industrial computed tomography. The microstructure of the impellers was characterized using SEM and TEM. Meanwhile, the mechanism of low temperature deformation was also discussed. All three impellers exhibited homogeneous microstructure with fine grains, and their mechanical properties were comparable to the level of wrought alloys; specifically, the tensile strength was about 1300 MPa, and the elongation was 20% at 77 K. In addition, many twins were found in the deformation zones, including the types of {\mathrm{10}\overline{\mathrm{1}}\mathrm{2}}, {\mathrm{10}\overline{\mathrm{1}}\mathrm{1}}, and {\mathrm{11}\overline{\mathrm{2}}\mathrm{2}}. PM-HIP impeller size was calculated using the finite element method in the modified Gurson model and compared with the size of the actual impeller. Dimensional shrinkage was consistent between the finite element simulation result and the actual part, and the deviation in the flow channel was < 0.3 mm.