Earthdam is widely used in water conservancy and water transportation projects because of its convenient materials and low cost，its main functions are flood control，power generation and irrigation. The temporary water and soil retaining dam（the second phase cofferdam）in the second line shiplock of Wan’an Junction is to assume the function of the original earth dam after the earth dam section near the upper sluice head is removed，and it is also an important temporary project to ensure the normal construction of the shiplock and the safety of the reservoir. Due to the influence of high water level in the reservoir area，the temporary water and soil retaining dam has higher requirements for deformation stability and seepage stability. As a temporary water retaining structure to maintain the normal operation of reservoirs and power plants during the construction of shiplock，its building grade is equal to the original earth dam（Grade 1 building），the quality standard of dam materials is the same as that of the original earth dam，and the project cost is higher than other construction cofferdams. In this paper，the characteristics of the design process，key point，engineering cost and other aspects are analyzed to provide a reference for similar projects.