Abstract: The settlement curve of the foundation endured the ramp load is a S-type curve, which is usually simulated via Poisson curve. Based on the Bayesian theory, a probability method was proposed to estimate the parameters of the Poisson curve. The results evaluated by the present method are the parameters’ posterior distributions, different from those of the traditional approaches. After calculating the parameters’ posterior distribution, the predictive distribution of settlement can also be obtained. The case shows that the results estimated by the probability method are more reasonable. The present method provides more parameters, and good for wide application.