In highway construction projects, the uneven settlement of roadbed caused by the abrupt change of geological conditions in different soil transition zones has become increasingly prominent problem. To solve the problem, a highway construction project in the transition zone between rock and sandy soil was taken as the background, based on the finite difference method, a numerical model of layered filling was established, and the settlement rule and the stress concentration effect of rock and sandy soil foundation were analyzed. The research results show that the subgrade settlement of the rocky section is small, and the maximum settlement is 2 cm, the subgrade settlement of the sandy soil section is large, and the maximu m settlement reaches 15 cm. In the transition zone between rock and sandy soil, obvious stress concentration occurs due to the abrupt change of soil properties, and the maximum settlement gradient reaches 1.2 cm/m, which is far beyond the allowable value of the specification. The construction sequence and the side-end effect have a significant impact on the settlement and stress distribution of the upper subgrade. Based on the research results, the improvement suggestions for subgrade settlement in different soil transition zones are put forward, the measures including setting the gradient transition layer, optimizing filling sequence and adopting geogrid reinforcement, which can reduce the settlement difference to the allowable range of the specification (<5 cm). The research conclusion can provide theoretical basis and technical support for the design and construction of similar projects, effectively reducing the settlement difference of subgrade in different soil transition zone, and ensuring the stability of the subgrade and driving safety.