The invention discloses an alumina roasting and SNCR (Selective Non-catalytic Reduction)-SCR (Selective Catalytic Reduction) combined flue gas denitrification technology. The technology is characterized in that flue gas in a main roasting furnace sequentially flows through a third-stage preheating cyclone barrel, a second-stage preheating cyclone barrel, a dryer and a first-stage preheating cyclone barrel and then is exhausted; an SNCR injection module is arranged between the main roasting furnace and the third-stage preheating cyclone barrel; an SCR reactor is arranged between the second-stage preheating cyclone barrel and a drying device; an ammonia injecting grid is arranged at an inlet of the SCR reactor; roasting materials are fed through a feeding port of the drying device, then sequentially flow through the first-stage preheating cyclone barrel, the second-stage preheating cyclone barrel and the main roasting furnace and finally is discharged through a discharging port of the third-stage preheating cyclone barrel. According to the technology, the technological properties of an alumina roasting furnace are combined; SNCR-SCR combination is adopted for denitrification, so that the denitrification efficiency is stable and more than 70-90%; NOx can be exhausted on the basis of standard; the ammonia escape is controlled to be less than 3ppm; the utilization rate of a reducing agent is increased, and the dosage of a catalyst is effectively decreased, so that the economic performance is improved.