In order to achieve the goal of “30·60” carbon neutrality,the advanced combustion technologies such as Oxysteam combustion can effectively reduce coal fired CO 2 emissions. For the new generation of OxySteam combustion technology,OxyCoal Combustion Steam System for power generation with nearzero emissions (OCCSS) can achieve nearzero emissions of coalfired CO 2. Using demineralized coal as a fuel can save dust removal equipment,and reduce the damage of the ash in the coal to the equipment. Research on the characteristics about the demineralized coal which is used for its combustion under O 2/H 2O conditions can provide a theoretical basis for subsequent combustion chamber design. A three step pickling method（HCL-HF-HCL）is used to prepare Zhundong demineralized coal. A high temperature tube furnace is used to prepare char at 900 ℃. The rapid heating O 2/H 2O combustion experiment at 950 ℃,5%，15%，21%，30% O 2 and 15%,25%,40%,60% H 2O(g) was performed by a micro fluidized bed O 2/H 2O combustion experiment system. Study the effect of H 2O(g) on the O 2/H 2O combustion characteristics of demineralized coal char under different O 2 concentration,and explore its promotion/inhibition law on the combustion process. Under the condition of O 2/H 2O combustion with rapid temperature rise of single particle (950 ℃),when the O 2 concentration range is 5%-30%,H 2O(g) has an inhibitory effect on the combustion process of demineralized coal. When the O 2 concentration is less than 21%,the H 2O(g) concentration change has a particularly obvious inhibitory effect on char combustion. When the H 2O(g) concentration changes from 0 to 60%,the conversion time of char under low O 2 concentration conditions (O 2 concentration:5%,15%) is 34.67 s and 23.22 s,which are 1.81 and 1.21 times of the 21% O 2 conversion time. In different H 2O(g) concentration intervals,the promotion effect of O 2 concentration on char conversion will be changed. When the O 2 concentration is less than 15%,the increase in its concentration can significantly promote the conversion of char. When the concentration of O 2 is greater than 15%,its effect is related to the concentration of H 2O(g). When the concentration of H 2O(g) is below 25%,the increase in O 2 concentration does not significantly improve the conversion of char.