Soil N loss by erosion on slope land is affected by soil mineral N loss mainly by runoff and organic N loss mostly by sediment. The process of soil nitrogen loss by erosion is restricted by interaction of soil nitrogen with rainfall and runoff. The interacting process of soil N with rainfall is divided into two stages: under rainfall conditions, soil N releasing process from soil to rain drops and soil N (mostly nitrite N) infiltrating process from top soil to deep soil in soil profile. Meanwhile, interacting process model of soil N with runoff is divided into three types, i.e. the mixed depth model of interacting process of soil N with runoff, the releasing and transporting model of soil N from topsoil to runoff and from upper slope to down slope, and process model of soil N loss by erosion. Based on analysis on interaction of soil with rainfall and runoff on slope land, the interacting models and mechanisms of soil nitrogen with rainfall and runoff are discussed to provide research methods and thoughts for further study on soil N loss by erosion.