Particle deposition onto a filter fiber was numerically simulated when a uniform external electric field was applied. The effects of electric field strength, particle inertia, and electrical conductivity of particles on particle deposition characteristics such as particle loading patterns and collection efficiency were qualitatively investigated. As a result, the electrostatic forces between a newly introduced particle and the already captured particles on the fiber were found to have a great influence on the particle deposition patterns compared with the results where the electrostatic forces were neglected. Conductive particles and filter fibers lead to higher collection efficiency and more linear structure of particle deposits than those of dielectrics, and the particle inertia could also be more important to the collection efficiency of a fibrous filter when electric fields are present. The simulated particle deposits obtained from this work agreed well with the existing experimental results, in which the photographs of particle loaded fibers, within an external electric field, were reported.