Oxygen carrier aided combustion (OCAC) technology has been recognized as a promising option for the combustion of high-alkali fuels such as biomass. By replacing inert bed materials in fluidized beds with oxygen carriers like ilmenite ore, both fuel combustion efficiency and oxygen utilization rates can be enhanced, while offering in-situ control of alkali metals responsible for ash fouling corrosion within the furnace. In this study, the absorption mechanism of potassium by Fe2TiO5 was investigated using a combination of experimental and theoretical approaches. To mitigate interference from impurities in the native ilmenite ore, relatively pure Fe2TiO5 was synthesized using the solid solution method, maintaining the same crystal structure as the native material. The capturing efficacy of Fe2TiO5 for potassium hinges on reaction temperature, with efficiency rising alongside temperature increases. Under oxygen potential influence, Fe can migrate to particle surfaces, forming vacancies. Based on the XRD characterization results, the crystal structures of Fe2TiO5 with different crystal facets and containing iron vacancies were modeled and optimized using Density Functional Theory (DFT) method. Furthermore, the binding configuration of potassium on its surface and the migration pathway within its interior were investigated. The formation of Fe vacancies requires overcoming an energy barrier of 2.38 eV, whereas the energy barrier for their migration in the bulk phase is even lower. In this context, the interaction between K and the Fe2TiO5(110) surface strengthens, reducing the energy barrier for migration into the bulk phase to below 2 eV, consistent with experimental observations.