Abstract: This paper deals with the ultimate bearing capacity of a foundation with soft clay underlying layer. Three sets of model test in laboratory show that the failure model in the foundation with soft clay underlying layer belongs basically to the punching shear failure. According to this, a formula for calculating the ultimate bearing capacity of this foundation is presented here. Being verified by the results of experiment and the analysis of a certain case history, this formula, in comparison with other relevant formula, will give a more satisfactory result within the range of condition H/B≤3.