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An improved airflow method to measure the distribution of adhesive strength between charged particles and a metal substrate in an external electric field is presented. In this study, toner particles were negatively charged with a corona charger and deposited on the substrate. The substrate with the particles on the surface was mounted in a rectangular air channel with parallel electrodes. Air velocity was increased at a constant rate, and entrained particles were detected by a laser particle monitor. By studying the relationships between particle entrainment efficiency and air velocity, the particle–substrate adhesion was analyzed in detail. It was found that particle adhesion increased with the increase in the initial charge of particles. It was also found that the particle adhesion increased in a vertically downward electric field but decreased in the upward electric field. These experimental results cannot be explained by the Coulomb force in the electric field. Therefore, a theoretical model based on charge transfer in the external electric field was proposed. This model explains the variation of the particle–substrate adhesion by considering the image force arising due to the transferred charges.