Variable section piles are gradually used in various engineering structures due to their unique bearing advantages, which have more complex forces and deformations than equal section piles. For the stability of super-long piles, the self-weight of the pile is also an important influence factor. Based on the cross-section structure of variable section pile, the deflection curve equation is constructed by segments, and the gravity is equivalent to the centralized load; the boundary conditions between segments are used to set up the differential equations, solve the equations and derive the recursive relation of the critical load of each segment, and then the optimal solution is obtained based on the genetic algorithm to compute the critical load of the n-section variable section piles. The reliability of the algorithm is verified by taking an offshore platform skirt pile as an example. At the same time, the optimal design of the section thickness of variable-section super-long piles is carried out based on the multi-objective optimization of genetic algorithm, and the optimization results are in line with the expectations.