The improved device of coke gasification reaction is employed to investigate the change rules of coke reactivity and strength after reaction, as well as coke microstructure, and pore size. Thermodynamic calculation is conducted to illustrate the imparity of the reaction between carbon with CO2 or H2O. The results show that H2O can promote the coke gasification reaction, and the coke reactivity (CRI) increases with the increasing φ(H2O), while the coke strength (CSR) has the opposite trend. The SEM observation results show that the interior and surface parts of cokes are all eroded at difference degrees after reaction, and the interior part of coke generates more large pores after reacted with pure CO2. While the interior part of coke that reacted with CO2 and H2O gas mixture generate more small pores, and the surface part is severely damaged. Moreover, the area percentage of oversized pores of coke gasified with gas mixture is larger than that of the coke gasified with pure CO2. The results of XRD indicate that the graphitization of coke increases after the reaction and reaches the highest when the reaction atmosphere is the CO2-H2O gas mixture, mainly due to the promotion of H2O to the consumption of isotropy.