Abstract: Given the widespread occurrence of antibiotics in natural water bodies and their associated ecological and health risks, this study comprehensively investigated the spatiotemporal distribution patterns, pollution sources, and risk levels of 22 antibiotics in surface waters of the Fujiang River (Mianyang section) within the Jialing River basin in the upper reach of the Yangtze River in 2023. Antibiotics and heavy metals were detected by ultra-high performance liquid chromatography tandem triple quadrupole mass spectrometer (UPLC-TQ-MS) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The results showed that the concentrations of antibiotics in the surface water of the Fujiang River showed significant seasonal differences. The total concentration of antibiotics in the dry season (mean 465.19 ng / L) was about 3 times higher than that in the wet season (mean 163.15 ng / L). Distinct spatial distribution patterns were observed: wet season concentrations showed minimal longitudinal fluctuations along the flow direction, whereas dry season concentrations exhibited a characteristic nonlinear "decline-rise-decline" trend. The concentrations of erythromycin, enoxacin, ofloxacin and lincomycin in the tail water of the sewage treatment plant in the wet season were 20 times, 8 times, 4 times and 2 times higher than those in the dry season, respectively. The highest total concentration of antibiotics was 2 times and 118 times that of the Yangtze River Basin and the Jialing River Basin, respectively. Pearson correlation analysis demonstrated significant associations between antibiotic distribution and multiple water quality parameters, including five-day biochemical oxygen demand (BOD₅), ammonia nitrogen, total nitrogen, electrical conductivity, turbidity, fluoride, and permanganate index. Notably, specific antibiotics showed significant correlations with As and Cu. Source apportionment identified livestock and poultry breeding wastewater as the primary pollution source, with supplementary contributions from aquaculture wastewater, domestic sewage, and chemical wastewater during the wet season. Medical wastewater emerged as a significant additional contributor during the dry season, indicating multisource composite pollution characteristics. Ecological risk assessment classified erythromycin as presenting moderate risk during the dry season and low risk during the wet season, while other antibiotics maintained low-risk levels throughout both hydrological periods. This study proposes to enhance monitoring of high-risk antibiotics (particularly erythromycin) during the dry season and to implement targeted management strategies for livestock farming and medical wastewater discharge. These findings provide a scientific basis for developing effective antibiotic pollution control measures in the upper reaches of the Yangtze River.