Abstract: As a case history, this paper introduces the design, construction and field observation of Shanghai Museum foundation pit, which is 135. 5m long, 90. sin wide, and 9m deep. The support system is a combined type of gravity retaining wall Which is constisted of Φ700 bore hole cast-in-place piles and cement mixing soil piles. Based on the obserbation data, the mechanical behaviour of the support structure, such as the earth pressure and pore pressure variation, the settlement and inclination of piles, and the positve effects of de-watering on the pit stability,is discussed. The conclusions obtained can be referred to in the design and construction of deep foundation in saturated soft clay.