Abstract: Based on the actual structure and heat transfer conditions of a 0.8MW boiler in a factory, the correlation law between the jet characteristics and the circulation characteristics of the flue gas furnace in the non-premixed combustion process of methane under the structure of the annular Venturi injector group is mainly studied. The simulation method explores the influence of fuel grading ratio and flue gas internal circulation intensity on the flow field, temperature distribution and nitrogen oxide generation characteristics in the furnace. Results show that there is an optimal value for the fuel grading ratio; excessive transfer of fuel heat load to the furnace will not only destroy the combustion stability, but also enhance the local high temperature and lead to an increase in the concentration of nitrogen oxides; without the interference of other factors, the larger the volume of smoke in the ejector, the better the effect of nitrogen reduction, and then it is difficult to describe the actual situation reasonably only by using the flue gas circulation rate ѡ index. Using the synergistic technology of large-scale fine gas classification and high-intensity flue gas internal circulation, a low NO_x combustion effect of less than 10mg/Nm³ can be achieved. The nitrogen oxide concentration at the outlet is reduced by 97.5%.