Abstract: The mechanical analysis of bottom hole assembly(BHA) isthe basis of BHA's design and well-path control in oil and gas drillingengineering. ``Beam-column theory'' is a typical and effective method inpractice, but its application is limited for not solving the initialbending problems. A method, as known as equivalent loading method, for solvingbeam-column with initial bending is discussed in this paper. The method hasbeen used successfully for solving practical problems in drillingengineering and provides theoretical foundations for downhole tool design andwell-path control. Conclusions are given in this paper.