Abstract: A single bubble growing model is established under subcooled flow boiling conditions in vertical rectangular narrow channel to numerically investigate the bubble growth. The model combines interface evaporation/condensation based on molecular dynamics and microlayer evaporation. The phase change model shows the multiple influences of micolayer evaporation under the bubble, superheated liquid near the heating wall, and subcooled mainstream. Numerical simulations results coincide with the experimental results well. The results reveal that the microlayer evaporation accelerates the bubble growth at the beginning, and the mainstream condensation keeps its size after the growing period. Details of bubble shape evolution and changes of microlayer thickness during the growth of the bubble are gained. It is found that the wall effect of narrow channel has an obvious effect on the bubble growing.