<p>The size of precipitated TiN particles exerts a crucial impact on the quality and mechanical properties of Ti-bearing ultra-high-strength steel. The conventional metallographic testing method for measuring TiN particle size suffers from low efficiency and delayed feedback, which renders it incapable of providing timely guidance for industrial production. In this study, a kinetic model for predicting TiN particle growth during the solidification and cooling process of Ti-bearing ultra-high-strength steel was established by comprehensively considering the microsegregation effect of alloying elements, the real-time varying solidification rate, and the differences in the initial growth size of TiN particles induced by homogeneous and heterogeneous nucleation. By employing this prediction model, the effects of cooling rate, cooling path and initial particle growth size on the TiN particle growth behavior were investigated, along with the distribution law of TiN particle size in continuous casting slabs. The results demonstrate that increasing the cooling rate, adopting a cooling path with weak intensity followed by strong intensity, and reducing the initial growth size of TiN particles can all effectively decrease the final size of TiN particles in the slab. The maximum size of TiN particles in the Ti-bearing ultra-high-strength steel slab reaches 9.26 <i>μ</i>m, which is located at the midpoint of the slab width and the position corresponding to 3/7 of the slab thickness. The TiN particle size at the slab corners is the smallest, not exceeding 0.85 <i>μ</i>m. This work provides a fundamental basis for the refined control of TiN particles in Ti-bearing ultra-high-strength steel cast slabs.</p>