The physical and mathematical models are established to account for the formation of evaporating thin liquid film and meniscus in capillary tubes. The core vapor flow is due to gradient of vapor pressure, which is mainly contributed by the shear stress at vapor-liquid interface. The liquid film flow is owing to gradients of capillary pressure and disjoining pressure. The heat transfer is composed of liquid film conduction and evaporation at vapor-liquid interface. The mass balance of vapor Row is considered to obtain the vapor velocity, this can evade directly solving the rarefied gas velocity field. In regard to the capillary tubes of micron scale, the calculation results show that, the bigger the inner radius or the,smaller the heat flow. the longer the evaporating interfacial region will be. There only exists meniscus near the wall, and nearby the axial center is flat interface. While as to the capillary tubes of scale about 100 mum, the evaporating interfacial region will increase with heat flux. Compared with capillaries of micron scale, the meniscus region will extend to the center of capillary axis. These can be tentatively explained as strong influence of the thin liquid film. For the capillary tubes of radius about 100 mum, the experimental results indicate that the apparent contact angles and meniscus profiles can almost coincide with those of the theoretical values.