The simulation of flow behavior of a two-component developer in an electro-photographic equipment is performed in order to obtain knowledge about the optimum design of a development system. The particle element method taking into account the magnetic interaction between developing particles is used and the validity of the simulation method is experimentally confirmed. The spike of a magnetic brush on a magnetic roll and-the shape change of the magnetic brush due to changes in the magnetic field are well expressed by the simulation. The effects of the parameters of the development equipment on the flow behavior of the developer, e.g. shape of the doctor blade, location of magnetic pole, etc., are discussed. The flow behavior of a developer changes with these parameters. There are optimum values in these parameters in order to avoid the fusion of toner particles and they are determined by the simulation. The proposed simulation gives very useful information for the design of a two-component development system.