Abstract: The purpose of this study is to investigate the failure mechanism and ultimate bearing capacity of subsoil under rigid and flexible foundations on red clay subsoil. Centrifuge model model tests and numerical simulations are conducted and some useful conclusions are drawn. The bearing capacity of a flexible foundation may be increased obviously compared to that of a rigid foundation. This increase, however, may also result in the increase of settlement. The displacements of subsoil under a flexible foundation become more harmonious, and therefore cracks develop later on locations far from the corner of the foundation as distributions become more dense and uniform. Compared to that of a flexible foundation, the slip surface of a rigid foundation is larger and deeper. The ultimate bearing capacity for a local shear failure may be determined when the vertical displacement of subsoil beside the foundation is transferred from continuous sinking to heave.