In order to solve the problem of high CPU usage and long rendering time in large scale terrain rendering in the flight simulator visual system,a GPU-based terrain tessellation algorithm is presented.We introduce an adaptive tessellation factor model combines screen-space projected area,terrain energy function and movement error function.This model conforms more closely to the hypsography,the velocity of viewpoint movement and the line of sight.And it separates the calculation of inside and edge tessellation factor in addition.We present a mesh refinement method which combines the PN triangles algorithm with displacement mapping based on mipmap and filtered-fBm.In practice,this method resolves aliasing and angularity in terrain mesh.The experimental results show that this algorithm renders high resolution terrain model in spite of coarse terrain mesh the CPU outputs.It can reduce redundant triangles and shorten the rendering time significantly without decreasing the rendering effect.