A model for a jetting fluidized bed gasifier is developed, treating the grid, bubble and freeboard zones in series. Reactions including char combustion, steam gasification, CO2 gasification and water-gas shift reaction are taken into account. The effects on model predictions of assumptions regarding the primary products of char combustion and char reactivity factor are analyzed by comparing the predictions with experimental data from a bench-scale jetting fluidized bed gasifier using different kinds of chars. Contributions of various reactions and different zones and phases to carbon conversion are analyzed.