A three-dimensional unsteady coal gasification model of BGL gasifier is established in this paper. The model considers the shrinkage process of coal particles, the coal core pyrolysis model, gas phase turbulence model, gas-solid flow model, gas-solid heterogeneous reaction model, gas phase homogeneous reaction model, energy conservation equation and phase-to-phase heat transfer model. This model fully considers the temperature and composition distribution of the three-dimensional space inside the gasifier. Through the optimization of the stoichiometric parameters of the coal pyrolysis section model, the CO/H2 molar ratio is about 1.59, which is consistent with the BGL furnace pyrolysis section operating mechanism; The three-dimensional unsteady simulation of the gasification section of the gasifier is used to simulate the composition of the outlet gas (CO, H2, CO2, CH4, H2O, O2) compared with the literature results, and the error is less than 4%, which proves the accuracy of the BGL model. Based on this model, we analyze the main parameters of the coal gasification process in this paper. The results show that the coal gasification efficiency increases with the increase of steam-oxygen ratio. When the steam-oxygen ratio is determined to be between 1—1.3, it can meet the process and production requirements, which is suitable for the characteristics of lignite used in this paper; the coal gasification efficiency will decrease with the increase of oxygen-coal ratio, but the content of effective gas in syngas shows a trend of increasing first and then decreasing. When the oxygen-coal ratio is around 0.17, the effective gas content will reach a peak value. With the increase of coal particle diameter, the temperature in BGL furnace decreases, the maximum temperature is dropping from 2536.77 K to 2047.81 K; as for the composition, the increase of coal particle diameter will reduce the production of CO, H2 and CH4, and increase the amount of CO2.