A sand sediment device for sewage treatment is disclosed, comprising a sediment tank, the upper end of the sediment tank being connected to a casing, the lower end of the casing being connected to a guide tube, and the lower end of the guide tube penetrating the top of the sediment tank and extending into the sediment tank. The casing and the sediment tank are connected by a drive unit to a stirrer, and the upper end of the stirrer is located outside the sediment tank. The upper end of the casing is fixedly connected to a support frame, the inner top center of the support frame is fixedly connected to a drive motor, and the drive motor is connected to the upper end of the stirrer by a lock-positioning mechanism. The lock-positioning mechanism includes a rectangular cross-section drive shaft, a square tube, a square bar and two lock-positioning components. The output end of the drive motor is connected to one end of the drive shaft through a coupling. In the present utility model, the stirrer and the driving motor are not in contact, and there is no need to overcome the resistance of the driving motor to the stirrer, thereby avoiding unnecessary waste of water flow energy.