Using an expansion of electrostatic potential in terms of partial solutions of the Poisson equations, a distribution of electrostatic field strength in a two-dimensional (2D) toner transfer system region between the toner and the paper has been calculated. The results have been obtained for a system in which photoreceptor and toner transfer element is a roller with a finite radius. In these calculations, the photoreceptor, the toner, and the paper have been characterized by the values of their thickness and dielectric permittivity. Results have been obtained when the transfer element is flat and when it is shaped as a roller with a finite radius. It is concluded that the one-dimensional (1D) approximation cannot be applied to calculate the electric field when the roller radius is close to or less than the radius of the cylinder-shaped photoreceptor. The limits of applicability of the dielectric thickness have been demonstrated.