In order to explore the settlement law during the construction and reconstruction of highway on site is obtained. With a view to providing reference for the settlement control of similar highways to widen the roadbed. subgrade, the pile number K1100+360 of the reconstruction and expansion project of Lianzhu Expressway was taken as the research object. The subgrade settlement was monitored by cross-section pipe, and the ABAQUS software was used to establish the extended embankment model for numerical simulation. The extraction settlement data was compared with the on-site monitoring to verify the validity of the numerical model, and sensitivity analysis was carried out on the height, severity and width of the subgrade. The results show that the larger the settlement value is, the larger the settlement is. The maximum settlement occurs under the vertical position of the new subgrade. The settlement of the subgrade is small and small in the middle. As the filling height continues to increase until the filling is completed, the settlement gradually decreases and tends to be stable. The measured maximum settlement value is close to the numerical simulation maximum settlement value, the error value is 1.23%, and the daily average settlement is less than the design specification of 5 mm. With the increase of the height, gravity and width of the fill, the self-weight stress of the fill increases, and the settlement becomes larger and then gradually decreases to be stabile. By comparing and analyzing the numerical simulation and the field measured data, the general law of settlement and deformation of the actual roadbed