As a new type of pile suitable for complex geological conditions, the application of Down the hole Jet grouting composite prefabrication Pile (DJC pile) in practical engineering is still in its infancy. When designing the scheme, designers need to rely on previous engineering experience, which is time-consuming and laborious. In view of this problem, this paper relies on a practical project in Zhejiang Province to carry out on-site static load test to analyze the variation characteristics of vertical bearing capacity of DJC single pile and composite foundation. Based on the test results, the genetic algorithm is used to establish the mathematical model of pile foundation optimization design. The total construction cost of DJC pile foundation project is taken as the objective function of optimization, and the corresponding calculation program is compiled. At the same time, the optimization design example of DJC pile composite foundation is given. The results show that the optimized design scheme reduces the project cost by 7% compared with the original scheme, and the foundation bearing capacity and settlement deformation still meet the design requirements, which provides experience for similar projects.