We propose an improved approach on visualization of large-scale terrain surface based on ROAM algorithm, within this approach, we study the issue in two aspects: one is view-dependent LOD(Level of Detail) control, the other is out-of-core data paging. An efficient data structure is introduced into the aspect of LOD control, on which coding method and none T-conjunction simplification algorithm is proposed. Meanwhile, the corresponding data conjunction method between different terrain blocks is given in the aspect of out-of-core data paging. The purpose of employing such a data structure is to improve the efficient use of internal memory. The experiment results show that our approach achieves real-time LOD rendering for sufficient large-scale terrain and saves much internal memory compared with traditional ROAM algorithm.