Abstract: The reaction rates of a bituminous coal ( Inner Mongolia) steam gasification with CaO additive had been studied with a pressurized fix-bed reactor through gas products analysis. The results show that CaO additive has a suffi- cient effect on char steam gasification rate,and the promotion effect of CaO on char steam gasification has a positive correlation with the mixing extent between CaO and char. Compared with non-CaO gasification,the steam gasification rate of char / CaO mixture which is the product of coal / CaO co-pyrolysis increases by 182． 34% . In addition,the steam gasification rate of the mixture of CaO and char that made of coal individual pyrolysis increases by 21． 13% . The de- gree of Ca2+ dispersion is the main factor which impacts char steam gasification rate. Furthermore,the reaction rate of char steam gasification with CaO additive has a positive correlation with Ca / C under the condition of Ca / C≤1． 0, while there would be a decrease in char / CaO steam gasification rate when Ca / C increases to 1． 2,compared with the condition of Ca / C = 1． 0. Temperature plays a sufficient role on char / CaO steam gasification rate. When temperature increases from 650 ℃ to 750 ℃ ,the reaction rate of char / CaO steam gasification increases by 594． 67% . When steam partial pressure increases from 0． 35 MPa to 0. 50 MPa and 0． 65 MPa,the char / CaO steam gasification rates increases by 95． 86% and 204． 14% ,respectively.