Abstract: Experimental investigation on the subcooled boiling heat transfer was carried out in a vertical up-flow double narrow annulus with 1. 5 mm gap. The working fluid is deionized water. The ranges of parameters as follows: pressure 0. 84-6. 09 MPa, mass flux 41. 9-300. 2 kg/(m2? s), heat flux 2. 61-114. 41 kW/m2. An empiric correlation used to predict the heat transfer of subcooled boiling in narrow annulus is induced from the experimental data.