Abstract: According to the ultimate bearing capacity control method, the effective length of a cement-mixed pile is calculated with the linear elastic-plastic load transfer function. Influence factors of effective length such as Poisson's ratio of soil, coefficient of rigidity of pile, elastic modulus ratio of the bottom soil and surrounding soil, pile's diameter, side ultimate displacement and top settlement of pile are analyzed. It can be seen that the factors have certain effects on the effective length except Poisson's ratio of soil.