Elastic-plastic finite element numerical simulation is performed to analyze the deformation characteristics of highway widened on soft clay ground when the interaction between new subgrade and old subgrade is considered. The results indicate that the construction of new subgrade leads to small settlement at the old road center and large settlement on the new subgrade, which exhibits a reverse basin shape. The subgrade settlement increases with the rise of subgrade height, and the maximum settlement at the top of new subgrade moves outward from the new subgrade center to new subgrade shoulder. The settlement also increases with the expansion of new subgrade width, and the maximum settlement at the top of new subgrade moves outward from the new subgrade shoulder to new subgrade center. Settlement after the construction would reduce as the precompaction period of new subgrade elongates, while increase as the construction shortens. A good insight into the settlement deformation behavior is contributive  to the determining of soft clay subgrade treatment and splicing scheme.