Abstract: The effect of variable viscosity on flow resistance characteristics of porous media with internal heat source was investigated.The experiments were performed on volumetrically heated porous media thermo-hydraulic test loop.Flow resistance characteristics of porous media are affected as viscosity of fluid is changed due to the changed temperature.The effect of variable viscosity on pressure-drop is prominent at high Reynolds numbers and it becomes weaker as Reynolds number increases.The difference of nondimensional pressure-drop curves between heating and adiabatic conditions is obvious at low inlet temperature.The difference becomes less significant as inlet temperature increases and all the curves are merged.New correction factors ξμ and ξCof Hazen-Dupuit-Darcy（HDD）model are presented and the relative error of pressure-drop factors between calculated values and experimental data is in the range of ±11.8%.