Interactive navigation of very large-scale terrain environment involves many difficulties because of its out-of-core geometric data and texture, which can not be wholly loaded into the internal memory. This paper puts forward a high performance technique for real-time walkthrough of the large-scale terrain environments. It performs geometric simplification within each terrain chunk during preprocessing and then generates a view-dependent continuous LOD of the whole scene with geomorphing at runtime. Both silhouette preserving and shading preserving criteria are satisfied by applying a new error metric-constrained normal cone to view-independent simplification. The generated models for rendering is more suitable to human’s perception than those by traditional geometric simplification criterion. Furthermore, the pre-extracted potential silhouette of each chunk can be used to construct the incremental horizon dynamically. This can prevent the ineffectual data from loading into the main memory and reduce the out-of-core paging and the number of triangles feeding to the renderer, thus lead to significant saving in interactive rendering. This paper also makes use of the advantage of GPU to generate lighting and shadow for large-scale outdoor environment, and balances the tradeoff between GPU, CPU and I/O through multi-thread.