Abstract: The nonlinear governing differential equilibrium equations of tubing buckling in straight wells are solved by the finite element method. The effect of tubing gravity is included. The assumptions of no gravity, constant pitch, and small displacement in traditional analysis are abandoned. The effects of different boundary conditions on the buckling of tubing are studied. The definition of helical buckling critical load of tubing in straight wells is given based on the finite element analysis. The influence of high order derivative of displacement on the value of drill tubing bending moment is studied. It is shown that the helical buckling critical load of tubing based on the theory presented in this paper fits well with the experiment result, and the high order derivative of displacement in the equation of tubing bending moment can not be neglected. An efficient method to predict the helical buckling critical load of tubing in straight wells of petroleum engineering is presented.