To study the mechanical characteristics of composite pile foundation at separated lock head，we establish a finite element model of composite pile foundation at separated lock head constructed on soft rock based on Jianzishan lock，analyze the deflections and deformations of the side piers，propose the simplification algorithm of pile top force，and research the influence factors of vertical load sharing ratio of soft rock ξV. The results show that the side pier is dominated by rigid body displacement，the lateral rotation and vertical axis torsion are the largest during the maintenance period，and the pile foundation layout should be dense outside and sparse inside. Because of the crushing zones，ξV is only 11.5%. The relation between ξV and replacement ratio may be approximated by a hyperbola，and the relation between ξV and the soft modulus by a power function. The smaller the pile spacing is，the higher the displacement rate，the higher the soft modulus，the smaller the pile-rock coefficient ratio，the higher ξV is. The consolidation grout treatment of the crushing zone can help increase the bearing capacity of the pile and improve ξV to 26.8% effectively.