With the continuous advancement of high-end equipment in the aerospace field, titanium alloy multirib components— characterized by their lightweight design, high load-bearing capacity, and high reliability are being  increasingly used as key load-bearing structures in aircraft. However, such components often exhibit complex rib arrangements and extreme combinations of size, which can easily lead to defects during forming, such as incomplete rib filling, folding, and flow line disorder, caused by undesirable material cross-rib flow. These issues also result in concentrated die stress and excessive forming loads. In this study, finite element simulation and a self-developed visual experimental platform for rib filling were employed to systematically investigate the material flow behavior, die stress distribution, and load characteristics during isothermal forming of two-dimensional three ribs characteristic component, three-dimensional connecting ribs characteristic component and large long strip-shaped multi-rib component. The results demonstrate that the use of optimally designed unequal-thickness billets enables quasi-synchronous filling of the rib cavities, effectively suppresses cross-rib material flow, improves forming accuracy, and significantly optimizes die stress distribution. Compared with equal-thickness billets, the optimized billets reduce the maximum forming load by 17.7% for 3D components and 28.3% for large-scale components, while notably mitigating stress concentration in the die.