This study is aimed to find operating conditions for maximizing yield of hydrogen in coal gasifier. CFD simulation was conducted for a Conoco-Phillips wet slurry 2-stage coal gasifier using discrete phase model(DPM) and finite rate/eddy-dissipation reaction model. Combustion in the first stage and gasification in the second stage were found to be well simulated using those models, and it was confirmed that activating steam reforming and water-gas shift reactions is a key to maximize the hydrogen yield, which means partial oxidation should be minimized. Additionally, more hydrogen was found to be produced when steam is injected to the area of higher temperature.