Abstract: Excavation collapses occur frequently, including the excavations supported by steel-braced retaining system. Due to the complex mechanics characteristics of the retaining structures, the influences of partial failures on the overall safety performance and progressive collapse mechanism of the retaining structures have not been studied. The model tests on the partial collapses caused by the breakage of retaining piles or struts are designed in this study, and the influences of partial failure or excessive large deformation of piles or struts on the earth pressures and internal forces in piles and struts are studied. When the partial failure or large deformation occurs in retaining piles, the influences of consequent soil pressure redistribution on the internal forces of the retaining structures in braced retaining system are different from those in cantilever retaining system, which causes greater additional internal force in braced retaining structures. When the struts are failed, the released loads will be intensively transferred to most adjacent struts rather than uniformly transferred to a large number of struts, which will easily trigger the progressive failure in struts.