The invention discloses a flotation system and a flotation method for a coal preparation plant, and belongs to production systems and methods for coal preparation plants. The flotation system comprises ore pulp pre-treating devices, flotation machines, a flotation cleaned coal defoaming barrel, slurry pumps, a scavenging cleaned coal defoaming barrel, a flotation cleaned coal dewatering device and a tailing thickener; ore pulp is conveyed to two front chambers of the three front flotation machines by the ore pulp pre-treating devices, so that coal slime can be subjected to rougher flotation; rougher flotation cleaned coal automatically flows to the flotation cleaned coal defoaming barrel, scavenging can be completed by two rear chambers of the flotation machines, and scavenging cleaned coal automatically flows to the scavenging cleaned coal defoaming barrel, is conveyed to the fourth flotation machine by the corresponding slurry pump and is subjected to concentration by the fourth flotation machine; concentration cleaned coal automatically flows to the flotation cleaned coal defoaming barrel and is conveyed the flotation cleaned coal dewatering device by the corresponding slurry pump to be dewatered; flotation cleaned coal can be finally manufactured, filter liquid flows back to the ore pulp pre-treating devices, tailings of the four flotation machines are conveyed to the tailing thickener, circulating water flows out of the thickener, and bottom flow of the thickener flows into a tailing coal slime dewatering device. The flotation system and the flotation method has the advantages that the flotation method is simple and is easy to implement, the quality of the flotation cleaned coal can be improved, and the treatment capacity and the efficiency of the flotation machines can be enhanced.