It is necessary to study the characteristics of water pollution in Oujiang Estuary. In this study, the temporal distribution characteristics of 17 water quality indexes in Longwan section in 2014-2018 were tracked, the limiting factors of water quality were explored by principal component analysis (PCA), and the single factor evaluation method was used to find the main pollutants in water quality. Then, water quality evaluation was combined with comprehensive pollution index method. The results showed that the water in Oujiang Estuary was alkalescence, concentration of TN was 0.93~3.68 mg/L, NH₃-N was 0.018~0.53 mg/L, TP was 0.005~0.205 mg/L and COD_Mn was 0.4~4.85 mg/L. The limiting factors of water quality in 2014 were pH and arsenic; In 2015, organic pollutants were easy to cause ecological risks; In 2016, the water body faced the risk of being polluted by multiple pollutants; In 2017 and 2018, water temperature, DO and NH₃-N were easy to cause algae growth. Oujiang Estuary water quality in 2014-2016 was class III, 2017-1018 was class II. The comprehensive pollution index was 0.17~0.32. This study is expected to provide reference basis for coastal waters of Wenzhou environmental management and planning, pollution prevention and control.