Abstract: Within the range of pressure from 23 to 28 MPa,mass flux from 350 to 1000 kg/（m².s）,and outside wall heat flux from 200 to 1000 kW/m²,experimental investigation was conducted on the heat transfer characteristics of supercritical pressure water in vertical upward annular channels.The effects of heat flux,pressure,mass flux and spiral spacer on heat transfer were analyzed,and two types of heat transfer deterioration occurred in the experiments were compared.The experimental results show that the heat transfer of water can be enhanced by increasing the mass flux or decreasing the wall heat flux.The effect of pressure on heat transfer is not uniform and depends on heat transfer form.It was found that the spiral spacer not only enhances the heat transfer of water,but also delays the heat transfer deterioration which occurs in high heat flux and low mass flux conditions.