Abstract: The open channel is the only flow passage for diversion and navigation in the second construction stage of TGP. The hydraulic prototype obsevation data obtaine in the four years after the operation of diversion channel are presented, including the flow pattern, velocity, fluctuation pressure, the ship sailing-tracking-line, etc.Compared with the model test results, it is concluded that the diversion channel is operated in a normal condition, and its design is successful;the compound crosssection is available for the main flow to be derived to the central part of the channel, but the characteristics of bending flow are very distinct and can hardly be changed.After enperiencing a few years flood, the open channel is proved to be safe and the navigation discharge has been raised than the original design.