Abstract: Experimental investigation on the heat transfer characteristics of the deionized water flow was performed in a narrow vertical rectangular channel. The cross-sectional dimension of the flow is 50 mm×2 mm. The experiments were performed with pressures at the inlet of the test section ranges from 0.1 to 0.3 MPa, mass flux ranges from 200 to 1400 kg?m-2?s-1, and heat flux ranges from 20 to 320 kW?m-2. The boiling curves and the heat transfer curves of water were obtained in narrow rectangular channel. Compared with 8 empirical correlations separately, and adopting similar theories and regression analysis, a new correlation is proposed for the narrow vertical rectangular channel in the subcooled flow boiling region. The study results show that in the narrow vertical rectangular channel, the heat flux shows the major enhancement effect as subcooled flow boiling happens, the Bertsch correlation predicts the experimental data best among those empirical correlations, and the new correlation predicts the experimental data well. Thus, the new correlation used in the paper is  applicable in the prediction of  the heat transfer coefficient of subcooled flow boiling in the narrow vertical rectangular channel.