A new model has been developed to predict the capillary limit of axial-grooved heat pipe. In the model the concepts of liquid saturation or liquid fraction of the cross-sectional area of groove,the modified relative permeability,absolute permeability of groove and Leverrt’s function are used. The Leverrt’s function is well represented by the functionf(s)=(1/√5)(1/s−1)0.175. In the model the effects of gravitational force, capillary force and viscous force are considered. The calculated results are in good agreement with existing experimental data reported in the literature.