Abstract: Heat transfer characteristics of singlephase turbulent flow in bilaterally heated narrow annular channels were studied and the theoretical model was proposed. Based on the present model, theoretical calculation was performed to predict the convective heat transfer characteristics for the developed turbulent flow in bilaterally heated narrow annular channels with gap sizes of 1.0, 1.5 and 2.0 mm, respectively. Calculations were found in good agreement with experimental data. The results show that the heatflux ratios, i.e. the ratio of the heating flux of the inner tube to that of the outer tube, have great influences on the characteristics of heat transfer during singlephase turbulent flow in bilaterally heated narrow annular channels. Whether the convective heat transfer is enhanced or deteriorated with reduced gap in bilaterally heated narrow annular channels depends on the combination influence of the heatflux ratio and the Reynolds number.