Abstract: The samples of fly ash from different positions along the flue gas of low-low temperature electrostatic precipitator were collected, and the particle size distribution was determined by laser particle size analyzer. The particle size, micro-morphology and chemical composition of flue gas were studied by scanning electron microscope (SEM), X-ray diffractometer (XRD) and X-ray fluorescence spectrometer (XRF). At the same time, energy dispersive spectrometer (EDS) was used to analyze the particles along the flue gas. The results show that the temperature of the flue gas decreases and the particles agglomerate obviously. the fine particles collide and agglomerate with each other in the flue gas to form larger particles, or are adsorbed on the surface of the larger particles, which increases the particle size and reduces the concentration of fine particles in the flue gas.Along the direction of flue gas, the color of fly ash gradually changes from grayish black to light yellow, the regularity of microscopic particles increases, and the final electric field fly ash is basically round or spherical; when the flue gas temperature decreases to the acid dew point, the SO₃ in the flue gas is absorbed by fine particles in the form of sulfuric acid fog, and under the action of internal diffusion, the fine particles coalesce and form larger particles. The content of Si in fly ash decreased gradually, while the content of Na, Mg, Al, S, Ca, Fe and P increased gradually. With the decrease of particle size, except for the relatively stable content of Ti, the content of Si and Al decreased gradually, while the content of C, K, Na and Ca increased.