Abstract: Based on actual measurement data of 23 field testing piles in 8 sites, an optimized fitting analysis of uplift load versus uplift displacement curves was carried out. According to the bearing characteristics of belled piles, Richards mathematical model, which was applied in biology, was selected to perform the fitting analysis. The fitting results of 23 field testing piles showed that the fitting has high precision with the correlation coefficient R being 0.99188 averagely, ranging from 0.97311 to 0.99942. The fitting effect was better than that of the hyperbolic model. Based on fitting equations, the calculated uplifting load has an error of comparing with measurements. The Richards mathematical model is accurate and feasible for the fitting of uplift load versus uplift displacement curves of belled piles.