To investigate the effect of liquid phase convective on the mass burning rate of medium scale pool fires, the liquid phase of pool fires was studied. A 3-D numerical model based on gas-liquid two-way coupling was used to model the pool fire. The gas phase and liquid phase were solved by large eddy simulation and direct numerical simulation respectively, taking into account buoyancy and Marangoni effects in the liquid phase. The heat and mass transfer between the two phases were calculated using a conjugate heat transfer method and an evaporation model. The proposed model was then validated by three pool fire experiments with different fuel sizes, fuel thicknesses and fuel types. The research results showed that the proposed model could accurately predict the mass burning rate of medium scale pool fires with a prediction error of less than 3%; in the development stage of pool fires, ignoring the Marangoni effect and buoyancy effect led to the maximum liquid velocity increased by 34.3%, the liquid surface temperature difference increased by 70.1% and the mass burning rate prediction error increased by 11.2%. In the stable combustion stage of pool fires, the buoyancy effect and the Marangoni effect had little influence on the instantaneous mass burning rate. With the increase of the diameter and the decrease of the depth of pools, the effect of the buoyancy effect on the combustion rate gradually decreased; Considering the descending process of the liquid level of thin-layer pool could reduce the prediction error of the combustion rate by 19.2%. In the numerical simulation, considering the liquid phase convective motion and the liquid surface drop process contributed to improve the prediction accuracy of the mass burning rate of medium scale pool fires.