Abstract: To clarify the regulation effects of polyaspartic acid (PASP) on nitrogen metabolism, absorption and utilization for flue-cured tobacco, the influences of reducing nitrogen application rate combined with applying PASP on the key enzyme activities of nitrogen metabolism, SPAD value, diurnal change of photosynthesis, nitrogen absorption, nitrogen utilization efficiency of flue-cured tobacco and nitrogen balance of tobacco growing soil were studied at different PASP application amounts (0, 2.5%, 5.0%, 7.5%, mass fraction) while reducing nitrogen application rate by 10%. The treatment without reducing nitrogen rate and applying PASP was taken as the control. The results showed that the indexes relating to nitrogen metabolism, absorption and utilization of flue-cured tobacco in all the nitrogen reduction treatments were lower than those in the control treatment. However, under the condition of nitrogen reduction, the activities of NR, GS, GOT and GPT in the treatments with different amounts of PASP increased compared with the treatment without applying PASP, and the increasing effect was the most significant in the treatment with 5.0% PASP. The SPAD value and net photosynthetic rate with the PASP treatment also increased in varying degrees, especially in the treatment with 5.0% PASP whose values were the closest to the control. The total nitrogen absorption, agronomic efficiency of nitrogen fertilizer, partial productivity, seasonal recovery rate and economic utilization rate of the PASP treatment increased significantly, while the apparent surplus and deficient amount and balance of nitrogen in tobacco planting soil decreased significantly. Among all the treatments, the treatment with 5.0% PASP was not only significantly higher than those with 0, 2.5% and 7.5% PASP, but also higher than the control. In conclusion, reducing nitrogen application rate by 10% combined with applying 5.0% PASP could promote the nitrogen metabolism, absorption and utilization of flue-cured tobacco and reduce the nitrogen surplus in soil.