Abstract: As an important infrastructure of open channel in water conveyance, hydraulic structures may affect the water quality of the channel by changing the hydrodynamic conditions and pollutant migration process.Taking the main canal of the middle route of South-to-North Water Diversion Project as the research object, the influence of hydraulic structures on the water quality of the canal was analyzed through the investigation and sampling at typical hydraulic structures such as inverted siphon/aqueduct and sluice gate.The results showed that: ① On the time scale, the seasonal differences of water temperature, DO, pH, permanganate index (COD_Mn), dissolved permanganate index (DCOD_Mn), particulate permanganate index (PCOD_Mn), total nitrogen(TN), dissolved total nitrogen (DTN), total phosphorus (TP), dissolved total phosphorus(DTP) and particulate total phosphorus (PTP) were significant (P < 0.05), while the seasonal differences of particulate total nitrogen (PTN) were not significant (P>0.05).On the spatial scale, the water temperature, pH, DO, COD_Mn and DCOD_Mn in the investigated canal showed a significant upward or downward trend (P < 0.05).② PCOD_Mn at the outlet of inverted siphon/aqueduct and other hydraulic structures was significantly higher than that at the inlet in summer (P < 0.05), but there was no significant difference in spring and autumn (P>0.05).In spring, the pH at the sluice gate was significantly higher than that in the water conveyance channel (P < 0.05), but there was no significant difference in summer and autumn (P>0.05).The research results can provide a basis for scientifically understanding of the water quality change law in large-scale open channels and optimizing water quality management.