The invention relates to an applying method of a slow/controlled release nitrogen fertilizer during cultivation of cotton bred in a feeding block. The total consumption of the slow/controlled release nitrogen fertilizer is 150-180kg per hectare of cotton in the terms of pure nitrogen, wherein 25-40 percent of the slow/controlled release nitrogen fertilizer is used for breeding the cotton in the feeding block, and the balance of the slow/controlled release nitrogen fertilizer is used for field production; a combination of a slow/controlled release nitrogen fertilizer with a controlled release period of 3 months and a slow/controlled release nitrogen fertilizer with a controlled release period of 4 months is selected for being used in breeding of the feeding block and field production respectively; and the slow/controlled release nitrogen fertilizer for breeding of the feeding block is uniformly blended in nutrient soil during breeding of the cotton, and the slow/controlled release nitrogen fertilizer for the field production is uniformly spread on the surface of soil in a field before the cotton seedlings are transplanted, and is ploughed and buried. The slow/controlled release nitrogen fertilizer is applied by using the applying method, and thus the growth and development of the root system of the cotton can be promoted, and the utilization rate of the slow/controlled release nitrogen fertilizer is increased.