The invention relates to a determining method of the reasonable oxygen enrichment rate of a blast furnace. The determining method is characterized in that aiming at the blast furnace with the effective furnace volume of 450-6,000 m<3> applying an oxygen enrichment process, in the daily production process, the blast volume, the spray-blow coal ratio, the volatile matter content of spray-blow mixedcoal powder, the grain size of the spray-blow mixed coal powder, the iron content of raw materials in the furnace, and the hot reactivity of coke in the furnace are taken as reference data to determine the reasonable oxygen enrichment rate of blasted hot air in the blast furnace. According to the operation indexes of the blast furnace in different stages, the mathematic correlation between the operation indexes and the oxygen enrichment rate of the blast furnace is built to determine the reasonable oxygen enrichment rate of the blasted hot air in the blast furnace, thus, stable operation of the blast furnace is achieved while production of the blast furnace is enhanced, and meanwhile, the effects of reducing fuel consumption and the production cost of iron making can be further achieved.