Abstract: Large variation of coal gasifier operation conditions can lead to substantial temperature change and possible oxygen existence in outlet syngas, which is harmful to safe and stable plant operation. A reactor network model for coal water slurry (CWS) gasifier was developed using Unisim Hysys based on the velocity profile of the gasifier, and a dynamic model was also built based on the reactor network model. The dynamic responses of temperature and outlet syngas composition regarding to CWS feed rate and concentration reduction were studied. The results show that the outlet syngas temperature is up to 2000℃ when the CWS feed rate reduces over 30%(wt) and the oxygen concentration increases observably. Meanwhile, the oxygen concentration of the outlet syngas is about 0.2%(v) when the CWS concentration reduces to 35%(wt). These results indicate that large variation in CWS feed rate and concentration should be avoided.