In hot rolling of large rings of titanium alloy (LRTs), the ratio of roll radii R1/R2, i.e., the ratio of the radius of the driver roll R1 to that of the idle roll R2, has a significant effect on the geometric shape of the deformation zone (GSDZ) which plays a decisive role in achieving LRTs with high quality. In the study, an analytical description of the GSDZ is presented, and quantitative relationships between the GSDZ and R1/R2 are determined. Then a validated coupled thermo-mechanical 3D-FE model of the process is developed in the dynamic explicit code ABAQUS/Explicit. Finally, an investigation is conducted regarding the effects of R1/R2 on the quality of LRTs from the view point of GSDZ using FE simulation. The results show that there is an optimized range of R1/R2 for obtaining LRTs with better end-plane quality and more uniform strain and temperature distributions