Abstract: Emission characteristics of fine particles and SO₃ were studied in Guohua Shouguang Power Plant No. 2 1000MW ultra-low emission coal-fired unit under 100%, 45% load and different NOx emission concentration, the distribution of water-soluble ion content in classified particles and the concentration of precursor SO₃ were studied. The results show that the emission concentration of PM₁₀ and PM_2.5 under 100% and 45% load does not exceed 0.92mg/m³ and 0.24mg/m³, respectively. With the decrease of load, the quality and quantity concentration of particulate matter decreased, but the particle size distribution did not change significantly. As the NO_x emission concentration increased, the concentration of particulate matter in some particle size decreased after SCR and ESP, especially the 0.006~0.0138μm, 0.0553~5.980μm particle size range after ESP. The water-soluble ions in the particles before and after SCR accounted for about 4% of the total mass, mainly contain Ca²⁺ and \textSO_4^2 - ; which increased to 39.5% before and after WESP, mainly contain Mg²⁺, \textSO_4^2 - , NH⁴⁺ and enriched in particles < 0.2μm. The migration of SO₃ in flue gas under different loads is basically the same. SCR and ESP will increase the concentration of SO₃, WFGD and WESP have an absorption effect on SO₃, and their emission concentration is 1.2~1.9mg/m³. The comprehensive removal efficiency is 45.2%~65.1%.