Abstract: A contour lines extraction method for 3D water body from LiDAR point clouds data is proposed in this paper.First,all points are divided into rough and equidistant grids whose number,average elevation and height standard deviation of every grid points will be calculated later.Then,confirm the grids belonged to specific water areas with strict conditions according to four characters of the point clouds in the waters: the low density,the similarity of elevation in all points,the weak echo intensity,water surface is lower than the surrounding land.Next,exclude sparse and discrete blocks through the connected domain by the character of larger water areas.Finally,re-organize point clouds data by fine-grid.Extract water areas with the seed filling method under more relaxed conditions starting from the grids belonged to the specific water areas.Experiments indicate that this method is feasible.