A gel-concentration dependent solution permittivity model is proposed for the first time, which is capable of fitting more accurately the experimental data in the literature than previous models, especially when gel concentration reaches ca. 3 wt%, which is not uncommon in practice. We show that gel polymer structure reduces the solution permittivity and raises the friction force acting on a particle, thereby reducing both its mobility and the degree of double-layer polarization (DLP), and interesting and important phenomenon in electrophoresis. If the viscosity of the liquid phase is sufficiently small and/or the hydrodynamic friction coefficient is sufficiently large, then DLP vanishes. This implies that the behavior of a particle in gel electrophoresis can be different both quantitatively and qualitatively from that in conventional electrophoresis.