Abstract: The differential equation for buckling of tubulars in horizontal holes under axial loads and the two end conditions that the equation should be satisfied are derived by energy variation principle. The deformation functions in sinusoidal buckling process of buckled tubular are determined by the energy method. It is proved that the equilibrium of buckled tubular is stable in the sinusoidal buckling process. Based on the theoretical method, the initial critical sinusoidal buckling load and the maximum load maintaining the sinusoidal buckling are determined. Numerical results are shown to be in good agreement with the theoretical predicfions.