The characteristics of soft clay roadbed settlement prediction model are studied in this paper. Firstly, based on one-dimension soil consolidation theory, the shape of time-dependent settlement process curve was analysed. Then, Mathematical analysis of traditional settlement models, including Gompertz model and Logistic model, was conducted, and the mathematical deficiency of above two traditional models were pointed out, which the settlement corresponding to inflection point has a constant ratio to the ultimate settlement. Further, Weibull model was proposed to describe the time-dependent settlement process of roadbed. This proposed model overcomes the deficiency of above two traditional models, and exponent model is one of its degraded expressions. Moreover, it can predict the total settlement processes of both the instantaneous load and the ramp load conditions. Finally, according to a group settlement observation data, the prediction results of different models are compared, and Weibull model has a good agreements.