The invention relates to a fertilizer for improving the carbon-nitrogen ratio of soil, used for tobaccos. Low-temperature biomass charcoal and high-temperature biomass charcoal are cooperatively usedto solve the problem of poor fertilizer conservation capability due to reduction of the ammonium nitrogen content of a 10-20 cm a soil layer when the high-temperature biomass charcoal is independentlyused in sandy soil and the problem of failed improvement of soil due to reduction of the bioactivity of the soil, caused by poisoning, induced by high increment of soluble organic carbon in soil within a short time, to microorganisms in the soil when the low-temperature biomass charcoal is independently used. When the high-temperature biomass carbon is independently used, the increase of active organic carbon in short-term soil is not significant; and when the low-temperature biomass carbon is independently used, the increment of the soluble organic carbon in soil is high in a short time, andpoisons the microorganisms in soil, reduces the bioactivity of soil, and the soil is not suitable for being improved.