Collecting a lot of data of terrain, water level, flow velocity and direction, this paper analyzes the sedimentation rule of Qingyanzi reach which is the fluctuating backwater area after the impoundment of the Three Gorges Reservoir. The following conclusions are drawn: 1) Since the water level exaltation and flow velocity palliation are less, deposition does not occur in general in Qingyanzi reach. This is different from the conclusion of the physical model experiment research; 2) Sedimentation mainly occurs in September and October when the water level is raising, most in Jinchuan moraine, Wuyangxi, Niushi moraine deep channel and Zhuozijiao; 3) Sedimentation area relates closely to the channel pattern; 4) Qingyanzi reach faces the transformation of channel pattern following the operation of the Three Gorges Reservoir.