【Objective】The leaching agent (ammonium sulfate) causes residues of ammonium nitrogen in the soil of ionic rare earth mining area.This results in serious nitrogen pollution in the soil and water bodies and destroys the ecological environment in the mining area. It also endangers the health of the surrounding residents and restricts the mining of ionic rare earth ore. However, the ammonium nitrogen pollution situation in ionic rare earth tailings and its impact mechanism are still unclear. 【Method】In order to understand the enrichment characteristics of soil ammonium nitrogen in the mining area and its influencing factors, we chose an in-situ leaching ionic rare earth mining area that has been closed for 4 years in Longnan County, Ganzhou City, Jiangxi Province. We sampled sites located on the different slopes of the hill. Soil samples were chosen from the soil surface to the bottom of the ore body, with a depth of 5.5 to 9.7 m. Ammonium nitrogen and other soil properties in the soil were determined. 【Result】The results show that soil ammonium nitrogencontent in the mining area ranged from 2.32 to 1056.44 mg·kg^–1, and was several times or even hundreds of times higher than in the natural and farmland soils. Ammonium nitrogen in the mining layers with rare earth was higher than in the upper soil, and with wide the variations among different soil layers in the vertical direction. Also, soil ammonium nitrogen content in the hill slope followed the sequence of top > bottom > middle slope. The correlation between soil ammonium nitrogen and the physicochemical properties of ionic rare earth tailings was observed to be different from the research conclusions of natural or farmland soil. Due to the supersaturation of ammonium in the soil, the distribution of ammonium nitrogen is not directly controlled by soil basic physicochemical properties which have an important influence on the ammonium nitrogen adsorption, such as soil clay, cation exchange capacity, etc. 【Conclusion】The major factors observed to influence ammonium nitrogen are the depth and amount of leaching solution inputting, and the permeability changes caused by the soil structure. Mining facilities such as leaching liquid pools, liquid collecting ditch, etc, affect the surrounding soil ammonium nitrogen content. Due to gravity, ammonium nitrogen will gradually migrates from the top to the middle and the bottom of the slope. This causes ammonium nitrogen to accumulate at the bottom of the slope over time. Under the leaching action of rainfall, a large amount of ammonium nitrogen in mining area soil will continuously migrate to the surrounding soil and water, which will harm the ecological environment in the long run. The results of this study are of great significance for improving the migration process of soil nitrogen in ionic rare earth mining areas and guiding the treatment of ammonium nitrogen pollution.