Nitrate loss is an important route of nitrogen loss, and its mechanism in flat cropland has been documented. However, it is still unclear how nitrate loss takes place in sloping cropland. Long-term plot experiments on field runoff were performed to monitor nitrate loss with runoff process in a sloping cropland of purple soil. Results show that runoff affected the process of nitrate loss from the slope cropland. Nitrate content in runoff increased at the initial period of a rainfall event, and then declined, and in the subsurface flow, it increased steadily and leveled off gradually. The potential environmental risk of the nitrate in surface runoff from slopeland of purplish soil is extremely high. The average nitrate content in surface runoff and subsurface flows of several rainfall events was N 0.73±0.17 mg L^-1 and N 21.72±2.05 mg L^-1, respectively. In about 75% of the surface runoffs, nitrate content was above N 0.5 mg L^-1 and in about 85% of the subsurface flow above N 10 mg L^-1. It was calculated that that the annual nitrate loss with surface runoff from the slope cropland of purple soil was N 0.93±0.05 kg hm^-2, accounting for 0.62% of the fertilizer N applied in the current crop season, while with the sub-surface flow, it was N 33.51±2.73 kg hm^-2, accounting for 22.34%, suggesting that nitrate loss via subsurface flow is the main route of nitrate loss from the sloping cropland of purple soil, not only leading to eutrophication of surface waterbodies and pollution of groundwater, but also aggravating environmental pressure in the upper streams of the Changjiang River .