The invention relates to a method for producing potassium chloride by using the direct flotation process of third solid sylvinite. The method comprises the following steps: third solid sylvinite materials are crushed into particles with the diameter smaller than 10 millimeters, water is added into the crushed materials for decomposition to obtain slurry, and the weight ratio of the materials to water is 3:1 to 3.3:1; a flotation agent and a restraining agent are respectively added into the slurry, after the mixture is mixed evenly, a closed process including one-stage rough flotation, one-stage of scavenging flotation and two-stage fine flotation is carried out to perform flotation, and coarse potassium chloride, fine potassium chloride, tailing potassium chloride and decomposition motherliquid are respectively obtained after filtration; the decomposition mother liquid is evaporated and cooled for two times to fully change into magnesium chloride products; after coarse potassium chloride is washed, filtered and dried, a potassium chloride product the purity of which is more than 90% is obtained. The method can realize the decomposition process under the condition of large granularity, and effectively saves investment and running cost of grinding devices and raises the productivity of potassium chloride.