The invention relates to a method for adding lime to alumina produced by adopting an ore-dressing Bayer process, in particular to a method for adding the lime in an original ore pulp mixing course in the ore-dressing Bayer process. The method is characterized in that an ore concentrate base flow is obtained after ore concentrate which is obtained after bauxite is floated is dehydrated by a thickener; and the ore concentrate base flow, the lime thinned by adopting a lime pulverizer, and a circulating alkali liquor are mixed to form standard original ore pulp according to the requirements of needed ingredients for [C/S], the solid contents and liquid phase Nk concentration. By adopting the method, the production flow is simplified, the labor intensity of workers is reduced, the bottleneck of production increase of the ore-dressing Bayer process is eliminated, and greater economic benefits can be created.