Abstract: This study used the Soil and Water Assessment Tool (SWAT) to simulate the transport and export of butachlor, a typical herbicide, under agricultural non-point source pollution conditions in the Caizi Lake basin. Model calibration and validation indicated satisfactory simulation performance. The results revealed pronounced spatiotemporal variation in butachlor export. Temporally, 79.32% of the annual butachlor load occurred between June and July, closely associated with intensive rainfall and increased runoff following herbicide application in May–June. Daily butachlor export was significantly and positively correlated with daily runoff (P<0.01, r=0.632). Interannual differences were also evident, with export loads in wet years (e.g., 2016) substantially exceeding those in dry years (e.g., 2018). Spatially, the lower sub-watersheds (sub-basins 13, 17, and 19) were identified as primary export zones, with markedly higher outputs than upstream areas. Among land use types, water bodies had a significant effect on butachlor export, whereas cropland and forestland showed relatively weak impacts, highlighting the retention and transmission function of pond networks in multi-pond systems. These findings provide a scientific basis for managing agricultural non-point source pollution and pesticide use in the Caizi Lake basin, with important implications for safeguarding watershed water quality and optimizing regional agrochemical strategies.