Abstract: bstract A co-evolution model and algorithm for optimized design of foundation pits is presented. This algorithm make use of characteristics which each subsystem is dependent with each other and has relationship between each other in the retaining and protecting system‚provides a co-evolution mechanism between the problem space and solution space‚and realizes collaborated optimization design for the scheme design and detail design.The experimental results of a “pile＋anchor” retaining and protecting system show that this co-evolution algorithm is effective and suitable for the optimization design of the retaining and protecting.