Abstract: The impact of the Three Gorges Dam on aquatic ecosystem and environment in the Three Gorges Reservoir Area (TGRA) has received international attention. Water quality is an essential factor to the ecological security and sustainable socioeconomic development for TGRA. By setting Zhutuo section in Chongqing as inflow and Nanjinguan section in Yichang, Hubei province as the outflow of the TGRA, the Mann-Kendall method was applied to test the inflow and outflow water quality trend with  the monitoring dataset (DO, CODMn, NH3-N) published by the ministry of environmental protection of the People's Republic of China from 2004 to 2017. The results showed that DO of the inflow and outflow sections remained class I and under a not significant upward trend. CODMn of inflow was under an upward trend while NH3-N was under a downward trend, either maintained class Ⅱ in recent years. CODMn and NH3-N of outflow had a significant downward trend and remained class Ⅱ in recent years. Compared to the inflow, the water quality of outflow was better and gradually improved. The mutation trend analysis showed that the water quality monitoring factors of inflow had a non-significant mutation, mainly occurred in 2005 and 2008. No mutation in outflow which indicated the water quality of outflow remained more stable than inflow. The concentration of DO, COD_Mn and NH₃-N are closely related to the characteristics of water situation, the production and lifestyle in the reservoir area. With the rising water level, declining water flow speed and sediment deposition, pollutant is sinking into the sediment effectively. In order to maintain and improve water quality of the Three Gorges Reservoir, the control and reduction in agricultural non-point source pollution, industrial sewage, urban sewage emissions and shipping emissions are in need.