Spatio-temporal characteristics of chlorophyll- a(Chl .a ) concentration and its influencing factors in Xiangjiaba Reservoir, Jinsha River during 2019-2023 were investigated using mathematical statistics, correlation analysis, stepwise regression and path analysis. The results showed that the annual average of Chl .a n Xiangjiaba Reservoir was 3.91 μg/L, and the annual variation of Chl .a was irregular. According to seasons, Chl .a as significanty higher in spring, summer and autumn than in winter. The Chl .a in the tributary was higher than that in the main stream. The annual average of Chl .a ncreased gradually from the upstream to the downstream of the main stream. The section with more population in the tributary had higher Chl .a . Pearson correlation analysis, stepwise regression analysis and path analysis showed that there were spatio-temporal variations in environmental factors affecting Chl .a n different years, seasons and sections. Pearson correlation analysis showed that Chl .a as extremely significant positively correlated with total phosphorus（TP）, orthophosphate（PO3-4 -P）, ammonia nitrogen（NH₃ -N）, nitrate nitrogen（NO^-₃-N）, total nitrogen（TN）, permanganate index（COD_Mn ）, air temperature（T）, water temperature（WT）, dissolved oxygen（DO）, pH, and extremely significant negatively correlated with transparency（SD）, conductivity（Cond） and current velocity（V）. Stepwise regression analysis showed that eight environmental factors (i.e., TN, PO³_-4-P TP, pH, DO, COD_Mn , SD and T) had significant impacts on Chl .a n the reservoir area. These environmental factors were positively correlated with Chl .a xcept SD. The path analysis decision coefficient showed that COD_Mn , TN and SD were the most important environmental factors affecting Chl .a . The final analysis showed that pH, DO, COD_Mn and SD were the passive factors affecting Chl .a , while TN, PO³_-4-P TP and other nutrients were the limiting factors, and temperature was the key factor. These results can improve our understanding of phytoplankton growth and nutrient status, and can provide a reference for studying the water environment of the Jinsha River cascade reservoirs.