Abstract: An algorithm is proposed to avoid the crack between terrain blocks,set the state of the border vertices consistent forcibly,at the same time set the ancestors of the se vertices active,which use the DAG （directed acyclic graphic） to decide the dependency relationship of vertices.The algorithm considers the impact to adjoining edge during disposing the border of blocks,and still maintains the grid regular characteristic.The experimental results show that our algorithm avoids crack effectively and fits for rendering parting terrain.