By simulating the saline-alkali soil environment，under the condition of reducing nitrogen fertilizer and applying biochar，the changes in enzyme activity of sugar beet rhizosphere soil，nitrogen content in rhizosphere soil，root vitality，root yield and sugar content of sugar beet were studied，the effect of biochar application on yield of beet under nitrogen reduction was clarified.The study could provide theoretical basis and technical guidance for planting sugar beet in saline-alkali soil environment to reduce nitrogen fertilizer application in the future.A total of 6 treatments were set up in the experiment，namely，salt-alkali stress total nitrogen treatment(CK)，saline-alkali stress applying biochar (BC)3% of the mass of air-dried soil with total nitrogen treatment(BC+N180)and 10% nitrogen reduction(BC+N162)，20% nitrogen reduction(BC+N144)，30% nitrogen reduction(BC+N126)，40% nitrogen reduction(BC+N108).The results showed that the soil enzyme activity and root system activity of sugar beet rhizosphere under the condition of biochar application and nitrogen reduction under saline-alkali stress were significantly increased compared with CK，in which soil urease activity increased by 14.9%～33.0%；phosphatase activity increased by 18.6%～54.7%；sucrose invertase activity increased by 16.5%～22.7%；catalase activity increased by 9.9%～12.2%；root activity increased by 12.3%～24.1%.In addition to 40% nitrogen reduction，the sugar beet root yield，sugar content and sugar yield of other treatments were significantly higher than those of CK.The sugar yield of 10% and 20% reduction treatments was not significantly different from the total nitrogen treatment.Under the conditions of this experiment，applying biochar of 3% of the mass of air-dried soil can improve the activity of soil enzymes，the sugar production of sugar beet，and the application of nitrogen fertilizer by 10%～20%.