The invention relates to kelp with ultrahigh iodine content, and a cultivation method and application thereof. The cultivation method of the kelp with ultrahigh iodine content includes: temporarily culturing kelp after seedling raising, disposing culturing rafts in a kelp farm, using kelp ropes to clamp the seedlings after picking out and separating the kelp seedlings, horizontally hanging the kelp ropes on the culturing rafts for cultivation, applying iodine fertilizer to the kelp during culturing, sorting, harvesting and airing when the kelp is mature, and obtaining the kelp with ultrahigh iodine content. By the biological nutrient enrichment technique, the biological iodine content of the kelp is increased evidently, and accordingly cultivation of high-safety kelp with ultrahigh iodine content is achieved. The kelp converted by biological concentration can be used as natural biological material for iodine supplementation, is high in safety, is widely applicable to various health foods, condiments, drinks and animal feed additives, has greatly reduced additive amount as compared with usage of common kelp, is especially applicable to special populations such as pregnant women, women in breast feeding, babies and the like.