Abstract: As an essential Yangtze river-connected lake regulated by the sluice and pump station, Gucheng Lake played a vital role in water resources regulation, drinking water supply, irrigation, aquaculture, and ecosystem balance maintenance. Temporal variation of hydrology regime and water quality between 2014 and 2020 in Gucheng Lake were investigated, and the effects of hydrological regime on water quality were also explored. Results show that: (1) The hydrological regime of Gucheng Lake was affected by inflow from Shuiyang River, local precipitation, sluice regulation and artificial replenishment. Compared with multi-years mean water stage, water stage in winter and spring increased by about 2 m. The period of annual lowest water stage was postponed from winter and spring to early summer. Natural hydrological regime was changed. (2) Multi-annual mean of TN, TP, NH₃-N and COD_Mn concentrations were 0.90 mg/L, 0.04 mg/L, 0.16 mg/L and 4.00 mg/L respectively. Concentrations of Chlorophyll a fluctuated around 0.01 mg/L. Seasonal Kendall trend test showed that nitrogen and phosphorus nutrients and COD_Mn witnessed a remarkable decreasing trend, while Chlorophyll a and nutrient index increased. Nutrient index shifted from mesotrophic status to eutrophication. (3) The water inflow of Gucheng Lake was significantly negatively correlated with transparency, and significantly positively correlated with TP, Chlorophyll a and nutritional index. Monthly average water level was significantly positively correlated with COD_Mn, NH₃-N and TP. Hydrological regime was the main driving force for the variation of water quality in Gucheng Lake. The capacity of water resources control and regulation was suggested to enhance further to meet water use for daily life, production and ecology during the nonrainy season and extremely drought condition. Strengthening watershed water pollution control and prevention was suggested to improve water quality in the rivers entering Gucheng Lake.