In order to investigate the effects of different types of gas and re-burning nozzle downward inclination angle on the combustion process of boiler,based on the FLUENT software,an ultra-supercritical 660 MW boiler was selected as the research object，and the re-burning gas coupled coal-fired combustion model has been built to  transform the boiler. A reburning zone was added at the upper part of the main combustion zone. The effects of different kinds of gas reburning and different reburning nozzle downdip angles on boiler temperature field,CO,CO2,O2 components and NOx emissions were studied. The results show that,the re-burning gas will make the main combustion zone temperature lower,and the flue gas temperature in the re-burning zone and the burnout zone increase. With the addition of re-burning gas,the center of the furnace flame moves up,and the temperature of the outlet flue gas also increases. The re-burning results in the increase of CO concentration at the furnace outlet,but the decrease of the concentration of O2 and CO2 and the significant decline of NOx emissions. Compared with the pure coal condition,the NOx emission reductions of straw gas,methane and biogas are 20.1%,26.2% and 25.2% respectively. The proper downward slope of the re-burning nozzle can improve the intensity of the flow field in the furnace,enhance the combustion effect of the boiler,and increase the residence time of the re-burning fuel in the re-burning area,and effectively reducing the NOx emission at the furnace outlet. When the downward inclination angle is 15°,the emission reduction effect is the best. The NOx emissions during re-burning of straw gas,methane and biogas are decreased by 31.73%,35.66% and 33.85%,respectively. The research methods and conclusions of this paper have certain realistic reference significance for the research and application of biomass gas and coal blending utilization in large coal-fired boilers.