Abstract: In order to improve the calculation level of the pollutant carrying capacity of the reservoir, in view of the problems that the existing calculation methods for the pollutant carrying capacity of the reservoir need more detailed hydrology, water quality, sewage outfall, and underwater topography which cannot be collected in place, and the pollutant mixing degree, eutrophication factors, pollutant concentration of stratified water temperature and other conditions which cannot be effectively judged in the model calculation method, an early warning method for the pollutant carrying capacity of the reservoir based on the least square method is proposed. Based on the analysis of water quality time series hourly data without significant heavy rainfall for 10 consecutive days by the automatic monitoring station for water quality of the reservoir, curve fitting of different water quality monitoring elements is carried out by using the least square method, and the change trend of hourly water quality data of the time series is analyzed, and the 5-day water quality hourly data is used for verification. The standard limit of water quality monitoring elements is used as the threshold value for early warning and reminding of the reservoir's pollution carrying capacity according to the Environmental Quality Standard for Surface Water, so as to effectively improve the reservoir's pollution carrying early warning capacity.