Well-known, that high-resistance materials have ability to accumulate a charge injected in them by an electron beam. It results in a deflection of the beam from a given trajectory. A model that describes a relaxation of the charge in a bulk of irradiated target is presented. Following relaxation mechanisms are involved in the model: diffusion, drift, processes of generation and recombination of electron-hole pairs and capture carriers on traps. Presented model gives a good opportunity to calculate an electric field in environmental space and a leakage current from a specimen. On the basis of comparison of simulation results with experimental data it is established, that the relaxation of a positive charge in organic dielectrics is determined by speed of a devastation of the traps located near to a surface of an irradiated target, and a relaxation of negative carriers - by more complex mechanism which is taking into account except for traps also Maxwell relaxation in a bulk of the specimen.