Abstract: To improve the fitting accuracy of Soft soil-Settlement model,by the analysis of measured data,studied the soft soil subgrade settlement development rule.The Logistic forecasting model and Gompertz forecasting model were superimposed on the basis of predecessor's research,and the L-G superposition curve model was set up in subgrade settlement,gave the approach of resolving the optimization model.By engineering project analyzed its fitting efficiency.By comparing the results of field observation data with calculation,not only the fitting accuracy of the new model is better than that of the Logistic model and Gompertz model,but the dependability of the combinational model is superior to each single model.The new model of L-G was scientific and applicative.It provides an effective analysis method for the inspected data of the settlement of foundation.