Abstract: Terrain walkthrough has been widely used in games，VR，simulation and GIS，etc．To interactively render terrains on large data sets，one must use efficient methods to cull and simplify the terrain data．But for dense data sets，current methods of view frustum culling and crack eliminating often lead to decline in performance．In this paper new faster methods are presented for block-based terrain walkthrough： a fast scanning is used for view frustum culling based on the projection of the view frustum on x-y plane；as for crack eliminating，elevation of the vertices which causes the crack is altered rather than splitting neighboring triangles——though it can cause Tjunctions．These methods are very fast．They require much less memory than traditional methods and hence can handle larger datasets as well as making interactive terrain walkthrough on PC platform possible with appropriate hardware acceleration．