A dynamic gasifier model including slag flow behavior simulation was established to simulate a new type of oxygen-staged gasifier recently developed in China. A reactor network model (RNM) is used to simulate the internal gas-solid reaction zone of the gasifier, in which the reactor is divided into several zones based on the understanding of the flow characteristics in the gasifier, with each zone represented by either a plug-flow reactor or a well-stirred reactor. This space division concept can provide a more reasonable temperature distribution prediction than one-dimensional models, without costing too much computational expense. In addition, a widely accepted slag layer model is used to simulate the time-varying slag accumulation and flow on the wall and the heat transfer process through the wall. Using the developed model, two kinds of oxygen-staged gasifiers were simulated: the refractory wall gasifier and the membrane wall gasifier. The RNM predictions were compared with industrial data and computational fluid dynamics (CFD) model results, and good agreement has been observed. The temperature distribution simulation results also showed that staged oxygen feeding can reduce the temperature near the main burner significantly, therefore extending the lifetime of the burner compared with that of without staged oxygen feed. Dynamic simulation results suggest that the dynamic response of the refractory wall gasifier is much slower than that of the membrane wall gasifier. In the membrane wall gasifier, the dynamic response of the syngas temperature and composition is rather fast compared to that of the wall temperature. However, for the refractory wall gasifier, the dynamic response of syngas temperature is as slow as that of the wall temperature indicating that different control strategies should be taken into account for better slag flow and syngas temperature control for these two kinds of gasifier.