Abstract: Precise quantification of sources of total phosphorus is important for assessing environmental risk in lake basins. In this study, we selected the Fuxian Lake Basin as an example and applied TP pollution load models to analyze the sources of TP at sub-basin scales from 1990 to 2020. We further used entropy weight fuzzy model to evaluate the dynamic pattern of environmental risk of TP pollution at the whole basin scale and sub-basin scale. The results showed that: （1）The TP pollution loads were from 59.38~239.05 t during the period of 1990~2020. Point pollution increased over time, whereas non-point pollution was still the dominant source. TP pollution was mainly from synthetic fertilizer and animal manure application on the crop land. Synthetic fertilizer was the dominant source in the Fucheng River and the Hewaizhigou River sub-basins, and animal manure application on crop land was the main source in Datikanqing River and the Dajing River sub-basins. （2）The environmental risk in the whole basin increased from 1990 to 2005 and reached a peak in 2005. Afterwards, the risk decreased from 0.56~0.06 during 2005 to 2020. The Hewaizhigouhe River and the Fuchenghe River sub-basins were always at a higher environmental risk level from 2000 to 2010 with the high evaluation value of above 0.55. Due to the closure of mining operations, a significant reduction in environmental risk was shown in the Dongdahe River sub-basin from 2005 to 2010. Compared to the whole-basin scale, environmental risk assessment at sub-basin scales provided more accurate information on lake management. Analysis of pollution sources and assessment of environmental risks at sub-basin scales can provide scientific basis and technical support for decision-makers in plateau lakes areas.