Based on the project of large internal digging harbor in Doha,and according to the engineering characteristics of the large foundation pit excavation,we analyze the key factors affecting the drainage engineering progress,i.e.the drainage design by combining the traditional foundation pit drainage design method and the modern finite element analysis technology,simulate the deep well depth and the distance between wells using the finite element software according to the actual situation and the design experience in the original specification,and put forward the optimum design,by which the reliability is improved.The results show that the application of numerical simulation technology plays an important role in saving the design cost and optimizing the design scheme.The design pattern which combines the traditional with the modern method may serve as reference for similar projects.