Abstract: The buckling equivalent length of a pile is not only used in the buckling of the pile but also one of the necessary parameter checking the material strength of the pile. In this paper, the equivalent lehgth about various boundary are obtained with the calculus of variations from the principle of minimum potential energy basing on the "m" method. The results calculated by our method in this paper are compared with those obtained by experiment, and further indicate that our method is precise. Moreover, various charts and formulas for practical uses are presented.