We have developed a numerical simulation method and used it to understand the control mechanism for separation discharges and toner scattering in the second transfer process. The second transfer process involves various materials, including paper, rollers, toner, intermediate transfer belt (ITB) and saw-like static charge eliminator. The simulation method takes into consideration electrical materials, geometric configuration and physical interaction among many factors: electric field, charge conduction, electric discharges, toner behavior, and ion flow field. The developed method was used to calculate the current characteristics, electric discharges, and toner scattering. Results showed good agreement with the experiments, and further calculation results showed that removal of electricity by static charge eliminator reduces toner scattering and separation discharges.