Abstract: In recent years, my country's economy has grown rapidly and the scale of road construction has continued to expand. To meet the increasing traffic demand, the implementation of reconstruction and expansion of the original road has become a key task. As a kind of lightweight material, foamed lightweight soil has the characteristics of low weight, environmental protection and vertical filling. Compared with EPS lightweight materials, foamed lightweight soil has better durability. Based on this, this article analyzes and discusses the application effect of cast-in-situ foam lightweight soil based on a comprehensive understanding of the characteristics of foam lightweight soil, combined with specific cases, in order to improve construction quality.