The genetic algorithm was used in optimal desingn of deep-mixing piles.The cost of deep-mixing piles in one unit area of foundation was taken as the objective function.All the testrains were listed following the corresponding specification suggestions were proposed and the modified genetic algorithm was given to deal with the problems of excessive computational cost and premature convergence.software system of optimal design of deep-mixing piles was developed in visual c++.The effectiveness of the optimal method was proved by an application example.