Abstract: Owing to the prestress loss particularity of the anchor cables in foundation pits, field tests are conducted. The distribution of shear stress on anchorage body is tested in the load tensioned process, and the prestress loss laws under different tensile loads and cyclic loads are analyzed. Through the numerical model of a project example, the prestress change laws of anchor cables in pit excavation process are considered, and the displacement and bending moment of supporting piles are compared between measures of a single tension and tension by steps. The results indicate that the debond slip in the front section of anchorage body is an important factor in prestress loss in tensioned locking process, and that the loss rate of prestress will be reduced under more cyclic tensile times and lower tensile force. For the supporting piles with multi-row anchor cables, the prestress of anchor cables in the upper row will be reduced by the tension of anchor cable in the lower row, and the anchor cable prestress shows a tendency of fluctuating increase throughout the excavation process. Through the control measures of tension by steps, the prestress loss of anchor cables is significantly reduced in the tensioned locking and excavation process, meanwhile, the force and deformation of supporting piles are more reasonable in excavation process. Such control measures can provide a reference for the construction of similar projects.