Abstract: A semi-circular foundation pit of Lingang metro station in Shanghai soft soil deposits is monitored and analyzed. Combined with the summarization of characteristics and advantages of the semi-circular pit, the deformations due to excavation are discussed. The monitoring results show that the ratio of the maximum lateral displacement of the retaining structures to the excavation depth ranges from 0.152% to 0.636%,and the mean value is about 0.325%. The deformation of the retaining structures exhibits a clearly deep bulging profile as the excavation continues, and the maximum lateral displacement of the retaining structures usually appears between 2 m and 6 m below the excavation surface. The ratio of the maximum surface ground settlement to the excavation depth is 0~0.587%. Under the same geological and construction conditions, compared with the rectangle pit, the semi-circular pit has the advantages of displacement control.