Abstract: In this paper, the excavation work of deep foundation pit for the north concrete anchor of south branch of Runyang Bridge is introduced. The pit is located at double stratums with the upper clay layer(16 m) and the lower sand layer(32 m).The depth of the pit is more than 48 meters. The diaphram walls with 12 inner braces and 32 piles are employed to support the pit, together with rows of chemical grouting curtain under them to hold back groundwater. At the same time, six deep well inside and two rows of deep well between the diaphram walls and outside chemical grouting are used to dewater the pit. During excavation of the pit, the forces in bracing system, the water level inside and outside the pit, and the deformation of walls have been monitored.It is shown that the design of the retaining structure is successful. It provides a practical reference for the design and construction of similar project.