The collection performance of wet electrostatic precipitators (ESPs) considerably deteriorates in the presence of ultrafine particles, which confer difficulties in realizing the ultra-low emission of particulate matter (PM). In this work, the use of a wet ESP combined with a perforated precharger was proposed to investigate its electrical and collection characteristics in flue gas containing ultrafine particles and compared these characteristics with those of the common wet ESP. Results indicated that the distributions of ion density and electric field were affected by ultrafine particle loadings. With increased PM0.1 concentration from 0 mg/m(3) to 100 mg/m(3), the average ion density of the common wet ESP decreased by more than two orders of magnitude. Meanwhile, the particle charging and transport performance deteriorated, even for large particles (10 mu m), and migration velocity sharply decreased by more than 85 %. The corona electrostatic field was significantly improved by installing the precharger. The combined wet ESP can be operated well even under problematic conditions. Additional electrons were generated by the corona discharge of the precharger, which contributed to subsequent particle capture. When the applied voltage of the precharger exceeded 15 kV, the electrostatic precipitation of 1 mu m particles only slightly weakened with increased PM0.1 concentration to 40 mg/m(3), and the capture of >5 mu m-diameter particles was nearly unaffected by ultrafine particles. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.