The invention provides a production process and a system of ultralow NOx emission of pellet flue gas. A set of flue gas circulation system is additionally arranged, the flue gas discharged from an airdraft drying section is taken as cooling air to be further conveyed to an air inlet of an annual cooling two-section, meanwhile, a reducing agent is sprayed at the top located at the annular coolingtwo-section, the reducing agent reacts with NOx in the flue gas subjected to the annular cooling two-section, and SNCR denitration is realized; and or the gas discharged from an air outlet of the annular colling two-section is conveyed to a preheating one-section of a chain grate machine after passing through a SNCR treatment system; the high-temperature characteristic of discharging the flue gasfrom the air draft drying section is utilized, meanwhile, the condition of high-temperature sintering ore in the annual colling two-section is utilized, and the part of the flue gas is treated by adopting the SNCR. By the adoption of the technical means, an enterprise atmospheric pollutant emission limit value on the production pressure of pellet roasting equipment requirements can be reduced to acertain extent, and the process and the system have the characteristics of being decreasd in investment, low in operation cost and remarkable in NOx emission reduction effect.