Titanium alloy large-scale rib-web components, known for their lightweight and high-strength properties, have the potential to substantially lighten the load-bearing components of aircraft. Isothermal Local Loading (ILL) has been recognized as an advanced technique for the integrated and less-loading forming of these components. However, material transfer in the transitional region during ILL often leads to folding defect near the die-partition line. To this end, the position of the neutral layer during ILL is calculated via the slab method, which is modified to align with the material flow in the transitional region, taking into account the multi-stage stress states under diverse boundary conditions. By utilizing this calculation model, the material transfer rate and rib-groove filling height can be ascertained. The material transfer rate serves as a criterion for predicting folding defect, and thereby an optimal billet is obtained and implemented in the ILL process. The results demonstrate that the material transfer rate is significantly decreased compared to the non-optimized billet, resulting in a non-folding component of transitional region.