Abstract: Coal gasification is a process in which coal or coal char is used as raw material,oxygen( air,oxygen rich or pure oxygen),steam or hydrogen are used as gasifying agents to convert organic matter in coal or coal char into gas fuel or downstream raw materials through chemical reaction at high temperature. In the process of coal slagging gasification,the organic matter in coal is converted into syngas,and the minerals are gradually transformed into solid ash after sintering and melting and then further converted into liquid slag. Because the organic matter in coal cannot be completely transformed in the process of gasification,there are unreacted coal char particles in the gasification slag,which leads to the formation of residual carbon in the gasification slag. The presence of residual carbon not only reduces the carbon conversion of coal gasification,but also has an important impact on the flow property of the coal ash. In this paper,the formation mechanism of residual carbon in ash and slag from slagging gasifier and the latest development of research on effect of residual carbon on flow property of ash and slag in recent years were reviewed. Firstly,the formation reason of residual carbon in coal gasification slag was analyzed. It is found that coal ranks and operation conditions are the main factors affecting residual carbon content in ash,while the interaction between residual carbon and slag determines occurrence of residual carbon in ash. In order to optimize operation conditions and reduce residual carbon in gasification ash,it is necessary to further study the influence of gasification conditions and ash composition on interaction between residual char and slag. Some researchers separated residual carbon by flotation and acid leaching to analyze its characteristic. Compared with low-temperature coal char,residual carbon in ash has less volatile,more pores,high graphitization degree and poor reactivity due to its high temperature and long residence time in gasifier. As an important component of ash,the presence of residual carbon significantly improves the ash melting temperature. In addition,the graphitization degree of residual carbon and the chemical composition of coal ash( Si/Al,Fe_2O_3 content) show great influence on the fusibility of coal ash containing carbon. The existence of residual carbon leads to formation of refractory minerals such as Fe Si,Si C and Fe. During the cooling process,the residual carbon promotes the crystallization of minerals in the slag and improves the viscosity of the slag. However,there is a lack of systematic study on the reduction rate of iron by residual carbon and its influence on crystallization behavior of mineral in different slags. Besides,residual carbon is prone to react with silicon and iron mineral. The temperature and rate of carbothermal reaction is influenced by composition of carbothermal reactants and diffusion of products. Thus,it is necessary to study the kinetics of carbothermal reaction under different gasification conditions.