A water treatment chemical-adding device integrating chemical preparation and addition is provided. The device includes a shell. A liquid distributing unit, a first screen cover and a second screen cover are disposed in the shell. The liquid distributing unit includes a plurality of liquid distributing plates disposed up and down and spaced apart. The second screen cover is fixed to a rotating shaft. The upper end of the rotating shaft penetrates a first through hole in the top of the first screen cover and a plurality of the liquid distributing plates in order and is rotatably connected to the top of the shell. The lower end of the rotating shaft is connected to an output shaft of a motor. The motor is fixed to the external surface of the bottom of the shell. A part of the rotating shaftabove the bottom of the second screen cover is tubular. The rotating shaft is communicated with a third liquid feeding port in the top of the shell. A part of the rotating shaft, which is corresponding to the second screen cover, is provided with a plurality of second through holes. The device integrates chemical preparation and addition and is high in working efficiency.