Abstract: The differential settlement and settlement control of the new and old road foundations are the important problem faced by the reconstruction and expansion projects in soft soil areas. In this study, the settlement monitoring of the new and old roadbeds in reconstruction and expansion of expressways is carried out. The settlement monitoring results are analyzed, the settlement of the new and old roadbeds is calculated by using the hyperbolic model, and the differential settlement control effects of different soft foundation treatment methods are evaluated. The results show that the cross section settlement of the old and new road foundations of the reconstruction and expansion of expressways presents "W" type settlement, that is, the settlement of the new roadbed at both sides is large, and that of the original roadbed in the middle is small. The settlement of the subgrade of the newly built road is large in the filling period, but small after entering the stable period. The filling of the embankment of the new road has small influences on the settlement of the old road foundation. Based on the hyperbolic model, the final settlement of the newly built roadbed is 82.52 mm, and it is 80.01mm in 15 years after construction. The final settlement of the old road foundation is 20.79 mm, and it is 19.15 mm in 15 years after construction. The best effects for soft soil subgrade treatment is to use PC pipe piles, and the differential settlement control of new and old subgrades after soft foundation treatment is significantly better than that of untreated subgrade.