This study introduced at first the background of numerous highway widening projects that have been developed in recent years in China. Using a large ground settlement simulator and a fiber Bragg grating (FBG) strain sensor network system, a large-scale model test, with a similarity ratio of 1:2, was performed to analyze the influence of differential settlement between new and old subgrades on pavement structure under loading condition. The result shows that excessive differential settlement can cause considerable tensile strain in the pavement structure of a widened road, for which a maximum value (S) of 6 cm is recommended. Under the repetitive load, the top layers of pavement structure are subjected to the alternate action of tensile and compressive strains, which would eventually lead to a fatigue failure of the pavement.However, application ofgeogrid to the splice between the new and the old roads can reduce differential settlement to a limited extent. The new subgrade of a widened road is vulnerable to the influence of dynamic load transferred from the above pavement structures. While for the old subgrade, due to its comparatively high stiffness, it can well spread the load on the pavement statically or dynamically. The test also shows that application ofgeogrid can effectively prevent or defer the failure of pavement structure. With geogrid, the modulus of resilience of the subgrade is increased and inhomogeneous deformation can be reduced; therefore, the stress/strain distribution in pavement structure under loading condition becomes uniform. The results obtained in this context are expected to provide a helpful reference for structural design and maintenance strategy for future highway widening projects.