The invention discloses a method for cultivating organic spirulina in large areas, which comprises the following steps: 1. the selection of a cultivation base; 2. choosing the concentrated solution of organic fertilizer with fine quality for use; 3. Cultivation; a track pool is added with enough purified water, the concentrated solution of the organic fertilizer according to the 1000: 1-5 weight ratio of the concentrated solution of the purified water and the organic fertilizer and spirulina seed; the photosynthesis is carried out on the spirulina by stirring; the cultivation is carried out; when per kilogram of culture fluid contains 0.5-0.7 g of spirulina dry powder, the collection is carried out; and the concentrated solution of the organic fertilizer is supplemented again; meanwhile, the carbon dioxide gas is filled till the pH value of the cultivate fluid reaches 8.5-9 to cause that the spirulina continuously grow; the steps are cycled in sequence. In the method, the chemical synthetic fertilizer or the chemical treatment are entirely not used or basically not used, thus fundamentally solving the problem of the chemical substance residue of the spirulina products and the overproof of the heavy meta; of the spirulina, guarantying the organic performance and safety of the spirulina powder and increasing the yield of the products.