In order to reduce CO2 emission from thermal power stations with keeping high thermal efficiency, a new concept of IGCC system, namely oxy-fuel IGCC, has been recently proposed. Hence CO2 is recycled in the system, the effect of CO2 recycle on eachequipments should be clarified. In this study, the effect of recycled CO2 injection on coal gasifier performance was investigated by means of three-dimensional RANS-based numerical simulation. For estimating of coal gasifier performance, coal gasification and water-gas shift reaction are key phenomena. Therefore, the partially active site sharing coal gasification model and detailed chemistry of watergas shift reaction model were implemented. Calculated gasifier was a commercial scale entrained flow coal gasifier whose coal feeding rate is 70 tons per hour. The gasifier consists of a lower combustor part and an upper reductor part. The effect of coal feeding rate into the reductor, R / T, was investigated. The results show that temperature in the combustor decreases with decreasing R/T. In the lower R/T condition, hence air ratio in the combustor decreases, the reducing atmosphere becomes stronger. As a result, coal gasification which is end othermic reaction in the combustor is promoted. Although coal gasification is occurred in the reductor in higher R/T condition, total coal gasification rate is not so promoted compared with lower R/T condition. Due to the above mechanism, the gasification performance becomes higher with decreasing R/T. The results obtained in this study indicate that it is important that how much the higher gasification reactivity in a gasifier is exploited by optimizing local heat balance.