Abstract The slag behaviors on the bottom cone are crucial characteristics that relate to the slag blockage in a gasifier. The slag flow and heat transfer model on the bottom cone was built to calculate the slag flow velocity, slag thickness and heat flux density. The results shown the slag flow velocity decreased and the slag thickness increased with the increasing cone angle. The slag heat flux density decreased with the increasing cone angle, and specially, the heat transfer rate of the overall bottom cone decreased significantly with the increasing cone angle. The flow slag residence time model was established to calculate the residence time distribution (RTD) of molten slag, and the results shown the mean residence time decreased with the increasing cone angle. In addition, this study preliminary analyzed the blockage possibility, and the results shown the slag thickness was significantly influenced by the critical temperature interval.