Interpreting the effects of representative agricultural measures on runoff nitrogen (N) loss in purple soil sloping croplands can help to provide the scientific basis for optimizing the preventive and control measures of non-point source pollution. During 2019-2021, in accordance with the recorded rainfall events grouped into different rainfall categories on the loamy purple soil sloping cropland originating from Shaximiao Group, the characteristics of runoff yield, the concentrations and losses of total nitrogen (TN), nitrate nitrogen (NO₃-N) and ammonium nitrogen (NH₄-N) in runoff under three representative agricultural measures including conventional fertilization (CK), optimized fertilization (T1), and optimized fertilization+straw returning (T2) measures were carefully examined. The results showed that compared with CK, the runoff depth decreased by 4.24% and 12.71% for T1 and T2, respectively, though these changes were not significantly different (P>0.05). The runoff coefficients in CK and T1 were equal and both 12.5% higher than that in T2 (P>0.05). TN concentration increased by 19.35% and 25.8%, and its loss increased by 11.54% in T1 and T2, respectively, compared with CK (P>0.05), indicating that the applications of T1 and T2 also have a potential risk of increasing soil N loss. Compared with moderate rain, heavy rain and large rainstorms, the runoff depth under rainstorms increased by 6.5%-191.11% (P<0.05), and the losses of TN, NO₃-N, and NH₄-N under rainstorms also increased by 106.38%-177.14% (P>0.05), 32.14%-360% (P<0.05), and 55.56%-600% (P<0.05), respectively. Additionally, compared with rainfall amount and runoff coefficient, runoff depth showed relatively stronger correlations with the study N loss variables (R²=0.32-0.76), indicating that runoff depth may be more suitable to describe the dynamics of N loss when developing the prediction models. Our results imply that the risk of soil N retention and inorganic N migration with runoff should be considered when optimized fertilization and straw returning measures are adopted.