Abstract: Based on numerical analysis and previous study results, a unified analysis model is established to estimate the ultimate bearing capacity of uplift piles with enlarged base. Under the limit state, it is supposed to form an elliptic local failure mode on the enlarged base, while in the straight shaft, a power function of slip surface is assumed. The failure curve is related to the soil properties and the pile sizes. A concept of H1 is presented, which is the height influenced by the enlarged base. It is an important part in the present method. Then, a formula applicable to the soft soil region such as Shanghai area is proposed to estimate H1. The calculated results are in good accordance with the field ones, proving that the present method is feasible. Moreover, it is also practical in calculating the ultimate bearing capacity of straight-shaft uplift piles.