Abstract: Based on the technical specification for retaining and protection of building foundation pit and strength theory for unsaturated soils, computational methods are constructed for embedded depth, displacement and inner force determination of retaining structure for unsaturated pit. The mechanical studies show that the functions of earth berm for unsaturated pit include two aspects. The first one is that the necessary embedded depth of the retaining structure can be reduced because of the longer force arm of the horizontal resisting force. And the second one is that the displacement and inner force of the retaining structure can be reduced for its horizontal elastic ssupporting. Analysis on an example illustrates that the construction method using earth berm in pit excavation together with lowering groundwater can decrease the embedded depth, displacement and inner force of retaining structure remarkably. Therefore, the construction method is economical due to sparing horizontal supporting structure as well as reducing project time.