Abstract: This study focuses on a small karst watershed named Xialaoxi in the junction zone of the middle and upper reaches of the Yangtze River in western Hubei, and in-site measurements of aquatic environmental factors, water sample collection and indoor experiments were conducted biweekly in 2019 for 15 observation sites, to investigate the spatial and temporal patterns of nitrogen and phosphorus concentrations and output loads from the watershed. The results showed that the total nitrogen and total phosphorus concentrations in Xialaoxi were (1.46±0.05) mg/L and (0.02±0.04) mg/L, respectively, which were generally lower than those in other rivers of the Yangtze River Basin. The nitrogen concentration was higher in spring and summer while lower in autumn and winter, and the phosphorus concentration was higher in wet season than that in dry season, which was closely related to rainfall. Nitrogen and phosphorus concentrations were higher in the upper reaches of the river, which were greatly affected by agricultural activities in the controlled watershed. There was significant spatial heterogeneity of nitrogen concentrations within the watershed. Phosphate concentrations were sensitive to human activities and domestic pollution near the river. The annual nitrogen and phosphorus loads of the watershed were 26.57 t and 0.25 t, respectively. They were mainly concentrated in spring and summer, contributing 82.0% of the annual nitrogen load and 83.9% of the annual phosphorus load separately. Nitrate and dissolved total phosphorus were the main forms of nitrogen and phosphorus loads, respectively. The proportion of particle phosphorus load to total phosphorus load in summer was significantly higher than that in other seasons due to rainfall erosion.