Abstract: In order to analyze the law of soil erosion, nitrogen and phosphorous losses , the experiments of soil erosion, nitrogen and phosphorus losses with runoff production were conducted under three use pattern grassland (traditional use grassland, enclosed grassland, no grazing grassland) of Hulun Lake watershed by artificial rainfall simulator. The results showed that soil erosion in traditional grazing grassland was most serious among the three use pattern grassland with the rain intensity as 40 and 75 mm/h. Under the same rain intensity, loss amount of total nitrogen was highest in enclosed grassland followed by traditional grazing grassland and no grazing grassland, while loss amount of total phosphorous was highest in traditional grazing grassland, followed by enclosed grassland and no grazing grassland. It was also shown that the relationship between the loss amounts of the nitrogen and phosphorous and the rain intensities was not significant under the same use pattern grassland. Building more enclosed grassland could prevent soil erosion effectively. A linear relationship was found between the emission load of nitrogen and phosphorus and accumulated runoff in traditional grazing grassland and enclosed pasture. However, an exponential relationship was found in no grazing pasture. The research could provide reference for the reasonable utilization of grassland in Hulun Lake watershed, the protection of water environment and the control of non-point pollution of Hulun Lake.