According to the result of simulated runoff experiment in laboratory, the impact of the mineral nitrogen's transport with surface runoff and leaching are analyzed. It is validated that the straw coverage can greatly decrease soil erosion and reduce the velocity of flow on the loess slope. Therefore, the interaction between soil nitrogen and runoff is prolonged, which lead to more mineral nitrogen to be dissolved by runoff. However, the total amount of the mineral nitrogen loss by runoff is reduced. Compared with the result of bare land, the straw cover can be concluded that the infiltrative depths and amount of water and soil nitrate are added.