【Objective】Understory cultivation of Panax notoginseng serves as a key agroforestry model for developing the forest-based economy. Investigating runoff, sediment yield, nitrogen (N), and phosphorus (P) loss patterns between P. notoginseng cultivation forestland and natural forestland under natural rainfall can provide critical scientific evidence for evaluating soil and nutrient loss in agroforestry systems, and optimizing understory medicinal plant cultivation. 【Method】This study took the Xiaodaohe Forest Farm in Boshang Town, Lincang City, Yunnan Province as the study area, using the in-situ observation experiment of field runoff plot to conduct fixed-point observations of runoff and sediment yield, as well as N and P losses of natural forestland (CK), 2-year-old P. notoginseng cultivation forestland (BP), and 3-year-old P. notoginseng cultivation forestland (KP) at different slope gradients (5°, 15°, 20°) in the rainy season of 2022. Then conducting significance tests for differences and correlation analyses on the amounts of runoff, sediment yield, N, and P losses under the various treatments. Building on these findings, this study further examined how slope gradient, rainfall characteristics, and their interaction influence N and P losses. 【Result】The annual runoff and sediment yields in plots BP and KP were 93.94%, 185.07% and 35.02%, 112.06% higher than those in plot CK, respectively. The total nitrogen (TN), total phosphorus (TP) and ammonium nitrogen (${\mathrm{NH}}_{4}^{+}-\mathrm{N}$) in the sediment were enriched, while there was no significant change in nitrate nitrogen (${\mathrm{NO}}_{3}^{-}-\mathrm{N}$). The annual losses of TN, TP, ${\mathrm{NO}}_{3}^{-}-\mathrm{N}$ and ${\mathrm{NH}}_{4}^{+}-\mathrm{N}$ in plots BP and KP were 97.23%, 141.92%, 88.8%, 88.14% and 67.82%, 137.39%, 66.65%, 48.06% higher than those in plot CK, respectively. Eroded sediment was the main pathway for TN and TP loss, while ${\mathrm{NO}}_{3}^{-}-\mathrm{N}$ and ${\mathrm{NH}}_{4}^{+}-\mathrm{N}$ were mainly lost with runoff. Rainfall amount and rainfall erosivity had the most significant impacts on N and P losses, showing extremely significant power function relationships with various loss amounts (P < 0.01). The nitrogen and phosphorus losses showed exponential function relationships with slope gradient, and the interaction of different experimental treatments, rainfall amount and slope gradient affected nitrogen and phosphorus losses.【Conclusion】Understory P. notoginseng cultivation significantly increased runoff, sediment yield, and N and P losses compared to natural forestlands. However, with the increase in the cultivation years of P. notoginseng, runoff, sediment yield, and N and P losses relatively decreased. This indicates that understory P. notoginseng cultivation is feasible, and the sustainable development of understory P. notoginseng cultivation can be achieved by reasonably adjusting the cultivation years and planting methods. In addition, attention should be paid to the impact of high-intensity rainfall and steep slopes on understory P. notoginseng cultivation to reduce the risk of N and P losses in the understory.