The heat transfer characteristics of steam condensation flow in a vacuum horizontal long tube were studied experimentally when the saturation temperature varies from 50 to 70 °C, mass flow rate is no more than 11 kg/(m²·s) and temperature differences between steam and cooling water are 3, 5 and 7 °C respectively. The tube wall is divided into filmwise condensation section and liquid accumulation section by the stratified interface. The local heat transfer coefficient in filmwise condensation section is significantly higher than that in liquid accumulation section. The local heat transfer coefficient increases with vapor quality and steam mass flow rate for all locations along the circumferential direction. The increase of temperature difference between steam and cooling water causes the decrease of local heat transfer coefficient in filmwise condensation section and has less effect on that in liquid accumulation section. With the change of steam saturation temperature, the local heat transfer coefficients in two sections of the tube appear different variation tendencies.