Abstract: Surface runoff is a major carrier of nitrogen and phosphorus loss, and the loss process is significantly influenced by rainfall intensity. However, the mechanisms underlying the different forms of nitrogen and phosphorus loss in runoff from purple soil sloping farmland remain unclear. We employed artificial rainfall simulation experiments to investigate the effects of three rainfall intensities (40, 60, and 90 mm/h) on the concentrations and losses of total nitrogen (TN), dissolved nitrogen (DN), particulate nitrogen (PN), total phosphorus (TP), dissolved phosphorus (DP), and particulate phosphorus (PP) in surface runoff on a 12° slope in the hilly regions of Chongqing City. We also examined the variation in DN∶TN and DP∶TP ratios. The results showed that with the increase of rainfall intensity, the cumulative runoff depth increased and the time threshold for runoff stabilization decreased. Rainfall intensity significantly affected nitrogen and phosphorus concentrations in surface runoff (P<0.05), with the highest average concentrations of TN and DN observed at 60 mm/h, while the peak average concentrations of PN and PP were reached at 90 mm/h. The DN∶TN and DP∶TP ratios were highest at 60 mm/h, with DN∶TN ratios exceeding 0.5 under all intensities, and DP∶TP ratios surpassing 0.5 only at 60 mm/h. The primary nitrogen loss pathway was DN, while phosphorus loss forms varied with rainfall intensity: PP dominated at 40 and 90 mm/h, and DP dominated at 60 mm/h. These findings highlight the impacts of rainfall intensity on nitrogen and phosphorus loss mechanisms in purple soil sloping farmland, providing theoretical support for soil and water conservation and agricultural non-point source pollution control in the hilly regions of the upper Yangtze River Basin.