Abstract: Study on axial stability of top-free and bottom-fixed pile acted by lateral friction and vertical concentrated load at the top is carried out by use of the energy method. A model for the pile partly embedded in Winkler subsoil is set up, the deflection function of the pile is given according to its boundary conditions, and the expression of the total potential energy of the pile-soil system is established. A series of formulas for stability analysis are developed according to the principle of the minimum potential energy, and critical slenderness ratio of the pile (λ_cr) is obtained by numerical method. Based on the results, a simple approximate formula of is λ_cr proposed. A numerical example is provided in the paper. It is shown that the resistance of the subsoil has important influence on λ_cr, and the lateral friction on the pile has less influence on λ_cr when the resistance of the subsoil is large.