Abstract: In design of inside lining of gasifier, the accurate determination of thermal conductivity of heatinsulation bricks is of key importance. Based on the porous characteristics of heatinsulation material and high seepage characteristics of hydrogen contained in gasifier medium, CFD simulations of microscopic heat transfer under 125 operating cases are performed by establishing a microscopic model. The quantitative correlation among the temperature, thermal conductivity of H2contained gas in blowholes and microscopic structure size is established. The method to estimate the apparent(actual) thermal conductivity of porous heatinsulation material in an environment of higher hydrogen level(φH2=45%—70%) is put forward. The simulation is confirmed by application in gasifier under commercialized operation with a smaller deviation(less than 6%) from actuallymeasured data and a higher reliability, which may guide the engineering design for the arrangement of gasifier lining of heatinsulation.