Abstract: The prestressed assemble steel support system (PASS) is an innovative retaining structure which can effectively increase the stiffness of connection joints between retaining piles and bracings. Compared with the traditional steel support, PASS can be used in larger and higher foundation pits. Basin excavation is proposed to solve the problem that the support system cannot be collided and compacted. The basic structure and principles of PASS are introduced firstly. Then a finished project in mucky soils is described in order to show the construction process of PASS. The monitoring results are also obtained, and unusual lateral displacement curves are found. It is proved by the back-analysis of monitoring data that the support stiffness much lower than the calculated one leads to the largest displacement at the top of retaining piles. The measures to ensure the full-strength connection in the joints are advised.