[en] The boiling heat transfer characteristics of downward steam-water two-phase flow in Φ 18 x 3 vertically tube are investigated experimentally at subcritical and near critical pressure. The experimental parameters are as follows: pressures p = 17.2-22.6 MPa, mass flow rates G 800-2000 kg/m²s, heat fluxes on the outside tube wall q₀ = 220-460 kW/m². It is concluded from the experiments that, in subcritical and near critical pressure region, the downflow boiling heat transfer is improved as pressure increases, but the heat transfer at supercritical pressures are some what worse than that at near critical pressures