Abstract: The new foundation design theory proposes a method for foundation design based on the p-s curves of base load and settlement with the principle of dual control conditions of strength and deformation. However, the corresponding p-s curves of different foundation sizes are also different. How to determine the reasonable sizes of the foundation according to the p-s curves of base load and settlement to meet the principle of dual control conditions of foundation strength and deformation is a very specific and meaningful work. The soil parameters are calculated based on the p-s curves of the in-situ plate loading tests. Then, the p-s curves of different foundation widths are calculated by the tangent modulus method, and the bearing capacities corresponding to different foundation sizes are obtained by the requirements of settlement and safety factor of foundation strength. Finally, combined with the foundation pressure to determine the minimum foundation size that meets the strength and deformation requirements, the proposed method is compared with the current codes of China through cases, which shows the rationality of this new method.