Interaction of biochar gasified in the mixed CO2/steam is still unclear. In this study, the interactions between biochar with CO2 (C-CO2) and with steam (C-H2O(g)) were systematically investigated using a TG analyzer and a tube furnace. Results show that the chemical reaction state and intrinsic ash were the essential reasons for the existing together of the three interaction effects between C-CO2 and C-H2O(g). Specially, an inhibitive effect occurred during the demineralized biochar gasified in the CO2/H2O(g) atmosphere, expressing that the C-CO2 was inhibited by the C-H2O(g) under the chemical reaction regime. A competitive effect was dominated the interactions of demineralized biochar-CO2/H2O(g) under either intra- or extra-particle mass transfer regime; while an evolution of “inhibition to competition” appeared under the diffusion reaction regime. The presence of intrinsic ash such as Ca element was conducive to the occurring of the synergistic effect