In this study, we developed a continuum theory of the charge transport in dielectrics by trapped electrons and holes, which takes into account two separate contributions of the current of trapped charge carriers: the drift part and the diffusion one. It was shown that drift current is mostly dominant in the bulk, while the diffusion one reaches significant values near contacts. A comparison with other theoretical models and experiments shows a good agreement. The model can be extended to two- and three-dimensional systems. The developed model, formulated in partial differential equations, can be numerically implemented in the finite element method code.