To explore different compost methods of straw returning on runoff, sediment and nitrogen losses in small watershed, a slope farmland in Erlongtan watershed in central Yunnan Province was chose as research object. Nine different compost methods of corn straw returning were set up: CK and 8 treatments. Each treatment included two straw return amounts to the field (0.75,1.5 kg/m²), two straw particle sizes (1,5 cm), two straw heap retting methods with urea reactor (water or water and urea stacking). In this study, the characteristics of runoff, sediment and nitrogen losses in a flue-cured tobacco slope farmland were studied. The results showed that: (1) In the 4 rainfalls with typical runoff, the application of higher straw return amount (1.5 kg/m²) and coarse grain straw (5 cm) could effectively reduce runoff and sediment losses in the slope farmland (10.06% ~ 38.60% and 10.07% ~ 38.60%). (2) The concentrations of total nitrogen (TN) and NO₃^--N in runoff under the application of lower straw return amount (0.75 kg/m²), coarse grain straw (5 cm), and compost with no urea were lower than those with higher straw amount, fine grain straw, and compost with urea (1.96% ~ 32.79% and 3.97% ~ 40.89%). (3) The proportions of NO₃^--N/TN, NH₄⁺-N/TN and PN/TN were 63.64% ~ 86.18%, 5.31% ~ 13.86% and 5.33% ~ 25.80%, respectively, and the main form of nitrogen loss in runoff on slope farmland was NO₃^--N, dissolved nitrogen was the main nitrogen pollutant in runoff. (4) TN losses concentration of sediment with the application of lower straw return amount (0.75 kg/m²), coarse grain straw (5 cm), and compost with no urea decreased (16.87% ~ 48.15%). (5) TN losses of runoff and sediment with the application of higher straw return amount, coarse grain straw and compost with no urea could effectively reduce the risk of nitrogen loss in the slope farmland in central Yunnan province (0.32% ~ 35.05% and 54.52% ~ 77.23%). Among TN runoff and sediment loss, runoff output was the main factor, accounting for 50.09% ~ 71.67% of TN runoff. In order to reduce the nitrogen losses in this watershed, higher straw returning amount (1.5 kg/m²) and coarse grain straw (5 cm) was recommended. Small or compost with no urea also could be applied according to different growth periods of flue-cured tobacco absorption and soil nutrient conditions.