In this research, we monitored carbon (C) and nitrogen (N) wet deposition, rainfall-runoff, and base-flow processes in Loess Plateau's dam watershed during wet season, in order to elucidate the contribution of C and N deposition to C and N loss in water body and discuss the distribution of C and N load in rainfall runoff, and then further evaluate the C and N losses during wet-season in the Loess Plateau. The results showed that the C and N wet deposition flux in this area reached 173.95 and 43.01 kg km^-2 mon^-1, respectively, whereas the C and N loss load by runoff were 11.52 and 2.19 kg km^-2 mon^-1, respectively. Therefore, the contribution rates of C and N wet deposition to the C and N loss by runoff during rainy season reached 65.81% and 100%, respectively, wherein the rainfall erosion contributed 59.20% and 56.16% of C and N loss, respectively. The rainfall erosion in Loess Plateau is mainly driving mechanism and the C and N loss mainly concentrated at the later stage of rainfall runoff, so if we take a measure to intercept the runoff at the later stage, nutrient losses will be effectively controlled. In addition, it is necessary to control nutrient loss according to local conditions to alleviate soil erosion and nutrient losses in the Loess Plateau's dam watershed.