The performance of a 300-MW-class Shell entrained-flow gasifier along with moisture contents in low-rank coal was studied by a rigorous dynamic model. The developed model predicted the steady-state reference data well. The gas and slag temperature profiles decreased with higher coal moisture content, which led to an increase of the slag thickness on the gasifier wall. The high-moisture coal resulted in reduced power generation together with reduced low heating value (LHV) of syngas, higher amount of oxygen supply, and less energy recovery in the membrane. The amount of coal required to produce the same total LHV of syngas was smallest when the coal was dried to 5% moisture. Therefore, the coal-drying level for appropriate power production was between 5 and 10%.