The flow in 180° turning pools was studied by a numerical simulation method, and the results showed that the mainstream flowed close to sidewalls, and big size recirculation areas appeared on both sides of the mainstream. This poor flow pattern was adjusted by setting rectifier plates, and the hydraulic characteristics of flow structure were studied. The results showed that the mainstream zone was in the middle of the 180° turning pool, and the velocity attenuation was significant after adding rectifier plates. Recirculation zone sizes and velocity values in the upstream of turning part were similar to those of general pools. For reflux zones of the turning part and the downstream, their sizes were reduced, and velocities were weakened.