Abstract: Chemical oxygen demand (COD) is an important aspect of agricultural non-point source pollution. Nine subtropical typical small watersheds were selected in Changsha County of Hunan Province. The characteristics of COD concentration and its spatial-temporal variation and their main influencing factors were analyzed using the five-year’s observation data (2011-2015). The results showed that: 1) The COD concentrations in the study area varied in a range of 0.31–42.63 mg/L and the average was 12.95 mg/L in the past five years. For the different types of small watersheds, the averaged COD concentration sorted in the following order: cropping-livestock > livestock > forest-cropping > forest. The COD concentrations were higher in summer and autumn than those in winter and spring, and generally increased from 2011 to 2015. 2) The monthly COD loads ranged from 3.15 to 1,086.6 kg/hm2, with average value of 152.06 kg/hm2. The characteristics of spatial-temporal and variation of COD loads were similar to COD concentrations in different watersheds. 3) The COD concentrations were significantly correlated with the densities of livestock and poultry as well as the resident population, with the correlation coefficients of 0.86 (p<0.05) and 0.69 (p<0.05), respectively. The COD loads were positively correlated with the livestock and poultry density, cropping area ratio, and runoff depth. The correlation coefficients were 0.87 (p<0.05), 0.69 (p<0.05) and 0.54 (p<0.05), respectively. Appropriate controlling the scale of livestock and poultry breeding, strengthening the domestic sewage treatment in watersheds, and promoting the recycling use of livestock waste are the critical approaches in reducing discharge of COD in the small subtropical watersheds.