Abstract: Abstract: A large hydropower project is located on the stream of Yalong River in China, and the multi-year average energy output of hydropower station is 1.6 billion kWh, having a total installed capacity of 360 MW. In order to protect the river ecology and environment, it is planned to build some facilities for fish passing, such as fishway. In order to be effective for a fishway, it is necessary for the migratory fish to find the entrance with as little delay as possible. The entrance to the fishway must be located at the furthest point upstream in the immediate area where fishes are congregating downstream the obstruction. It should not be positioned either in the center of the river or too far downstream. The attractivity of a fishway is linked to its location in relation to the obstruction, and particularly to the location of its entrances and the hydrodynamic conditions (flow discharges, velocities and flow patterns) in the vicinity of the entrances. In other words, successful fishway design requires the close combination of fish biology and hydraulics. Combined with specific engineering, the primary goal is to establish a new idea and method for location choice of fishway entrance. Based on the resources, biology and ecology in the Yalong River, the migratory fishes in the river are divided into 4 categories, and the Schizothorax oconnori, Schizothorax macropogon and Schizothorax waltoni are the main migratory fishes in present study. Through analyzing the swimming abilities of the main migratory fishes, it is found that the regions where the velocity does not exceed 1.2 m/s are fit to install the entrance. In present study, it is first offered that the regions where the velocity ranges from 0.4 to 0.8 m/s are the optimal to install the entrance. And, given other factors, the regions where the velocity is 0.8-1.2, 0-0.4 and 1.2-1.5 m/s are the alternative locations of I, II and III respectively to install the entrance. It is forbidden to install the entrance in the area where the normal velocity exceeds 1.5 m/s. Taking a large hydropower project as the example, the hydraulic characteristics of the velocity and flow field at downstream were analyzed. When the power units were running, there was complex flow pattern in the tail channel, with some circulation and backflow. The maximum and minimum velocities near the left bank at downstream of tail channel were 1.5 and 0.8 m/s, respectively. It was also shown that the migratory fish could travel as far upstream as possible along the left bank. Because of the high velocity at the end of tailrace, the fishes were impossible to pass. It is therefore advisable to install the entrance to the fishway near the tailrace. Considering the velocity and flow pattern, there was backflow region at upstream that was also the situation of the stake number 0+200, which was the obstruction for migratory fishes. In addition, the average velocity near the bank was all larger than 1.1 m/s, which indicated the migratory fishes could not congregate in this area. It was pointed that the optimal location of entrances was the area 200-210 m away from the axis of the dam at the downstream, where the velocity and flow pattern conditions were fit to set the entrance to the fishway. And some fishway entrances should be arranged above the power station generators for standby. Accordingly as an inter-disciplinary subject, the choice of fishway entrance is not perfect. In the further, the study should be developed combined with the special life habits of migratory fish.