The invention discloses an apparatus and a method for dewatering slime through competitive absorption. The apparatus comprises a slime concentrating machine, a first slurry pump, a buffering barrel, a second slurry pump, a drum-type mixer, a vibrating screen, a first belt transporter, a dryer, a cyclone dust collector, an induced draught fan, a second belt transporter, a buffering bin, a feeder and a third belt transporter. According to the method, strong-viscosity high-mud-content slurry, which is underflow of the slime concentrating machine, and a crowd of container bags filled with a drying medium are fully mixed, so that water in slime is competitively absorbed by the drying medium, and slime is indirectly dried; the mixture of water-reduced slime and the container-bag crowd is separated by the vibrating screen, the container-bag crowd is sent to a dryer for drying, and after regeneration, the container-bag crowd is sent to the buffering bin and is sent to the drum-type mixer by the feeder for recycling; and the dryer is connected with the cyclone dust collector for preparing a dewatered slime product. The dewatering efficiency of slime in coal preparation plants is effectively improved, and the economic value of low-rank slime is improved. The apparatus and the method are especially suitable for dewatering of strong-viscosity high-mud-content slime. The structure of the apparatus and the method are simple, easy to realize, good in dewatering effect, high in safety and low in operation cost.