The dynamic multiphase flow in ironmaking blast furnaces (BFs) operation is a transient-state process, but it was widely modeled as steady-state in the past. It is necessary to understand the evolution of in-furnace phenomena after some operational parameters are changed. In this study, for the first time, a transient-state BF (TBF) model is developed to describe the dynamic in-furnace phenomena in terms of flow, thermal, and chemical behaviors, featuring respective chemical reactions in respective burden layers. The TBF model is validated against the measurements from an experimental BF. Then the TBF model is applied to a commercial BF of industry-scale and used to capture the time-evolution of velocity field, cohesive zone profile, thermal field, and gas utilization efficiency from an initial state to a steady state under given conditions. Moreover, the TBF model is used to study a specific BF operation change – hot burden charging, for TBF model capability demonstration, by capturing the time-evolution of the in-furnace phenomena at certain time intervals. It shows that, after charging the hot burden, the change of reacting flow can be more significant in the upper shaft regions compared to other regions, more important at near-wall region compared to the center region, and this largely happens in the first 8–10 h; besides, top gas temperature can rise to ∼ 800 K and coke rate is increased by ∼ 20 kg/tHM to maintain the BF productivity. This TBF model offers a cost-effective tool to understand the evolution of in-furnace behaviors in operation changes; and provide a basis for real-time understanding and control in future ironmaking.