Abstract: The iron ore sintering process is the main source of NO_x emissions and accounts for about 48% of the total NO_x emissions in the iron and steel industry. The generated NO_x is mainly from fuel consumption, and it usually exists in the form of quasi-particle in iron ore sintering bed. Therefore, it is important to deeply understand the combustion characteristics and NO_x formation mechanism of quasi-particles in iron ore sintering process. Based on this, the effects of coke breeze particle size, presence of an adhering layer of quasi-particles, adhering ratio of quasi-particle, and coke breeze content on the mass conversion rate of different types of quasiparticles and conversion rate of fuel-N to NO_x were investigated in a vertical quartz tube reactor in detail. The results show that the mass conversion rate decreases with increasing coke breeze particle size for S'- and S-type quasi-particles; the conversion rate of fuel-N to NO_x decreases with increasing coke breeze particle size for S'-type quasi-particle and exhibits the opposite trend for S-type quasi-particle, which is because of the presence of an adhering layer consisting of fine iron ore and limestone. Considering the combustion characteristics of S-and S'-type quasi-particles, the presence of an adhering layer of quasi-particles favors the increase of mass conversion rate and conversion rate of fuel-N to NO_x. The mass conversion rate and conversion rate of fuel-N to NO_x both decrease with increasing adhering ratio for C-type quasi-particles whose adhering layer consists of fine limestone and coke breeze. For P-type quasi-particles comprising coke breeze, fine limestone, and fine iron ore, the mass conversion rate decreases with increasing coke breeze content. The conversion rate of fuel-N to NO_x is not linear and reaches the lowest value when coke breeze content is 50%.