In this study, the effect of the hydrogen supply on combustion performances and emission levels of low calorific value coal gases has been numerically investigated in a model combustor. The numerical modelling of turbulent diffusion flames has been performed by using a CFD code. k-epsilon model of turbulent flow, the PDF/mixture fraction model of diffusion flame and P-1 radiation model were used in the present study. The flames of coal gases for pure and hydrogen supply cases were modelled to predict its combustion behaviours. There are five cases of testing, i.e., pure generator gas or pure blast-furnace gas and fuels supplied 4%, 5%, 10% and 15% hydrogen by mass. According to the predictions, the combustion performances of generator and blast furnace gases were improved by supplying hydrogen progressively. Similarly, NOx formations of generator and blast furnace gases were increased due to increment of its flame temperatures depending on hydrogen amounts.