A three dimensional modeling of large-scale terrain and city includes not only the surface elevation grid construction but also the modeling of the various features in the scene, such as rivers, buildings, lakes, forests and so on. Henceforth, the data required are usually large, and are referred to a lot of sorts and forms. In the traditional approach to realize the whole scope of the 3D terrain virtual walkthrough, modeling is a larger workload and the fast modeling is not easy to be achieved. In this paper, the powerful speciality of Terra Vista about terrain modeling and the unique character of OSG(open scene graph) on the field of 3D rendering are proposed. According to a citys large scale terrain 3D walkthrough system, the paper presents how to convert the different data sources to the supportive formats in Terra Vista to achieve the fast modeling, then to implement the fluent virtual walkthrough of the whole scene using the excellent 3D rendering ability of OSG.