Numerical simulation was made to the section of Luanhe County, Luanhe River, where there are the major pollutants of nitrate nitrogen, by the software Feflow. And in the meantime, solvend fitting verification and simulation forecast to the data of monitoring well were made. The results show that the groundwater in both sides of the river is polluted unclearly around the upstream before the mountain; after the river runs out of the mountain, the groundwater along the river banks is polluted at a certain degree; the groundwater in downstream is polluted more seriously than the one in upstream. We can forecast that the clay barrier will make the diffusion of pollutants in the groundwater slowdown gradually in the coming 5 years.