Based on one foundation pit support in deep soft soil region, the cement-soil framework suspended in the soft soil is designed as the foundation pit retaining structure. Through orthogonal test with factors of the width of retaining wall, the depth of embedding and the thickness of reinforced soil at the bottom pit, it can optimize the design parameters of foundation pit and solve the construction difficulties of soft soil foundation. This provide a reference for similar foundation pit design. In the foundation pit retaining engineering of deep soft soil region, the reinforced soil of pit bottom and the gravity wall of foundation pit sidewall form the retaining structure of cement-soil framework suspended in the soft soil layer. This structure can effectively control the deformation of foundation pit and ensure the stability of foundation pit during construction. The calculation scheme of foundation pit design by orthogonal test table can effectively reduce the number of trial calculation and improve the efficiency of foundation pit design. The variance of test results shows that the reinforcement thickness of bottom pit can reduce around 80% of the top wall horizontal displacement, the top wall vertical displacement and the bottom pit uplift, which plays a key role in controlling the deformation of foundation pit.