Coal fired power generation is positioned as part of base load power supply in our country and high thermal efficiency is required to overcome its high carbon emission. Recently, a new concept of IGCC system as a future technology is proposed that utilizes steam genereated by heat recovery of gas turbine exhaust for low-temperature steam gasification to improve the thermal efficiency. This research focused only on a entrained gasifier with steam supply, and gasification performances were evaluated using a one-dimensional numerical analysis that considers heat and material balance with gasification reaction rates. As a result, a paticular condition was found that improves cold gas efficiency by an appropriate control of oxygen comsumption and steam supply.