Slope gradient has many impacts on soil erosion by water and mineral nitrogen loss in an erosion process.The results from artificial rainfall experiments are as follows.Only in a certain range of slope gradient,the amounts of soil erosion and mineral nitrogen loss aggrandized with the increase in slope gradient.Exceeding the range,how ever,the amounts of the losses decreased.With the same slope length,the crit ical slope gradients for soil erosion and mineral nitrogen loss were validated between 15 and 20.Soil mineral nitrogen loss showed two trends.First,soil mineral nitrogen loss by runoff was much more than that by sediment,being about 99% of the total loss amount.Second,soil nitrate loss in erosion process was the maint rend, being about 96% of the total amount of mineral nitrogen loss.The percent of nitrate lost in surface runoff was much more than that in sediment.Further measures to reduce runoff flow are suggested to control soil mineral nitrogen loss by surface runoff.