Abstract: Within the range of pressures from 9 to 22MPa, mass velocities from G 600 to 1200kg/（m²·s）, and heat fluxes from x 0 to 1.0, experiments had performed to investigate the frictional pressure drop of the steam-water two-phase flow in a six-head internally ribbed tube with the outer diameter of 38.1mm and the thickness of 7.5mm. The test section was thermally insulated as horizontal direction. Based on the experimental results, it was found that pressure had a noticeable effect on the frictional pressure drop of the mental results, it was found that pressure had a noticeable effect on the frictional pressure drop of the steam-water two-phase flow, and the frictional pressure drop factor of the steam-water two-phase flow decreased with an increase in pressure. The frictional pressure drop factor of the steam-water two-phase flow tends to one near the critical pressure. As steam quality increased, the frictional pressure drop factor of the steam-water two-phase flow first increased, and then it had a decreasing tendency. With an increase in mass velocity, the frictional pressure drop factor of the steam-water two-phase flow decreased. Correlations of the frictional pressure drop factor of the steam-water two-phase flow had been provided.