Based on the dataset of 120 water quality monitoring sites (including 16 coastal sites) in rivers along Liaodong Bay, the principal component analysis-multiple linear regression (PCA-MLR) model was used to study the pollution characteristics and flux of organic matter, nutrients and heavy metals, and analyze their possible sources. The pollutants exceeding the first grade of Environmental Quality Standards for Surface Water were COD_Mn, AN concentration. TP concentration and TN concentration, and other water quality parameters met the standard. The TN/TP ratios were high and seriously deviated from the Redfield ratio. The input of high N and low P load from terrestrial sources was the main factor causing the increase of TN/TP in Bohai Sea. DO concentration, EC, AN concentration and TN concentration in non-flood season increased significantly than in flood season, while pH, turbidity, COD_Mn and TP concentration in non-flood season decreased significantly than in flood season. The concentrations of organic matter and nutrients in estuaries were affected by factors such as the agricultural areas that rivers flowed, while the concentrations of heavy metals were related to the distribution of industrial enterprises in the region. The annual fluxes of TN, TP, COD, AN and petroleum pollutant into Liaodong Bay were 3.63 × 10⁴ t, 1 608.5 t, 14.8 ×10⁴ t, 3 086.6 t and 221.9 t, respectively, and the fluxes of Hg, Cd, Pb, As and Cr⁶⁺ were 0.264 t, 0.253 t, 1.978 t, 20.434 t and 31.651 t, respectively. According to their contribution, the main pollution sources were domestic sewage and industrial wastewater, sources caused by hydrological factors (hydrodynamic conditions, etc.), water-gas interface pollutants exchange and secondary sources, non-point sources of farmland runoff and transportation.