The LOD model based on quad-trees is improved on the basis of former researches. This model is applied to manage and organize terrain data. Node judgment rule is established to determine the detail degree of the present visual area. A new bidirectional way was given to recover the cracks according to distance. By programming, this method is proved to be able to generate multi-resolution terrain model continuously, improve the efficiency of terrain navigation, and realize smooth transition of the models with different resolution.