Preparation of micropowder by the combination of jet milling and electrostatic dispersion is an innovative method. By means of this method, it can achieve the dual goal of producing fine powders and maintaining the dispersiveness. While, the electric charge carried by particles will vanish gradually when refined powder is stored in air, which lead to that the dispersion effect of charged particles will weaken and even disappear. In this paper, a model of electric charge decay of charged particle in air is established, the influence of particle size, relative humidity of the atmosphere, relative permittivity and initial q/m i.e. charge to mass ratio of charged micropowder on the decay process are evaluated. In addition, the non-contact measuring experiment is designed to verify the simulation results as well. The results indicate that the q/m of charged particle decreases as exponential relationship with the storage time, the remained q/m and its decay rate of particle with smaller size is lower during the whole process. The decay rate of charged powder increases with the increase of relative humidity in air. Particles with higher relative permittivity has a lower decay rate of charge, and the decay rate of particles with larger initial charge to mass ratio would also be higher. The numerical results of the model could reveal the rules in electric charge decay process well in general. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.