Abstract: Bubble lift-off diameter model is one of the most important sub-models in the field of two-phase flow and numerical computation method. In order to study the influence of different forces on bubble lift-off, theoretical analysis was carried out about the force equation of a single bubble in subcooled flow boiling, which proposed a dismensionless model for the prediction of bubble lift-off diameter. The comparison between predictions and experimental data, which involved water and R113, was made and the changing rule of bubble lift-off diameter as dimensionless numbers was analyzed. The results show that the predicted lift-off diameters agree well with the experimental values of water and R113. Bubble lift-off diameter increases with Ja and decreases with the increase of Re, Ca, Pr and Ar. Combined with the definition of dimensionless numbers, it is concluded that the growth force and the surface tension force restrain bubble from departing the wall, which results in a larger lift-off diameter. The shear lift force and the buoyance force promote bubble to depart, causing the decrease of lift-off diameter.