In order to satisfy the application requirements of the large space transportation systems in china， the 130 L helium cylinder is firstly developed by superplastic-isothermal forming method using Ti-5Al-2.5Sn ELI titanium alloy plate， and the cryogenic temperature deformation mechanism of Ti-5Al-2.5Sn ELI titanium alloy is also systematically investigated in this work. The experimental results indicate that Ti-5Al-2.5Sn ELI titanium alloy shows the cyclic deformation behavior of sliding and twinning modes under 20 K， and the incomplete re-crystallization of raw material can be eliminated by thermal forming process. Furthermore， the completely recrystallized grains with equiaxial characteristic and the curved grain boundaries of helium cylinder can coordinate cryogenic temperature deformation process nicely， inducing the excellent mechanical properties of Ti-5Al-2.5Sn ELI titanium alloy under cryogenic temperature. Therefore， the superplastic-isothermal forming method is a feasible technology to manufacture the large pressure vessel for the aerospace industry.