In order to investigate the characteristics of twophase flow resistance in packed porous media, the experiments of airwater twophase flow in packed beds with spherical particles of different sizes are performed by the test facility of DEBECO (Debris Bed Coolability). Based on the experimental data, the calculative results by different predictive models are compared and verified, and the influence of interfacial drag on pressure drop for twophase flow is analyzed emphatically. The results show that the effects of the interfacial drag on twophase flow pressure drop are negligible for packed beds with smallsize (e.g. d=1.5mm) particles, and the twophase flow pressure drop curves show an increasing tendency with the increase of air flowrates. The interfacial drag has significant influence on twophase flow pressure drop for packed beds with largesize (e.g. d=6.0mm) particles at low liquid velocities , and has a descentascent tendency in the pressure drop curve.