Abstract: This study investigates the emission characteristics and evolution of fine particulate matter from two 1000 MW ultra-low-emission coal-fired power units in China. Based on online operational data, together with fly ash sampling and characterization at the inlet and outlet of the electrostatic precipitator (ESP) and at the stack outlet, the emission behavior of fine particles under variable load conditions ranging from 350 to 800 MW was systematically analyzed. The results indicate that coal blending ratios significantly affect the emission characteristics of fine particulate matter, and high-ash coal blends increase the operational burden on the ESP. Distinct ESP responses to load variation were observed between the two units, primarily attributed to differences in electric field structure design, secondary dust control ability and daily operation and maintenance of the two units, highlighting the critical roles of design operating conditions and actual operational characteristics (e.g., particle re-entrainment) in governing fine particulate matter control behavior. Submicron particles (0.5~1.0 μm) constituted the primary penetration size range. In the wet flue gas desulfurization (WFGD) system, significant differences in synergistic particulate removal efficiency were observed between the two units (35~94%). High-humidity flue gas conditions (12~14%) enhanced slurry droplet entrainment and reduced the nucleation energy barrier, thereby substantially promoting the condensation and formation of sulfate aerosols. Field sampling and particle characterization further revealed that the ESP exhibited relatively low collection efficiency for difficult-to-charge submicron aluminosilicate particles. Needle-like sulfate crystals detected in the emitted flue gas were attributed to the formation of condensable particulate matter (CPM) under high-humidity conditions. This work further elucidates the coupled mechanisms among coal blending, load variation, ESP, WFGD and CPM formation, providing a theoretical basis for optimizing particulate control systems and mitigating fine particulate matter emissions from coal-fired power plants.