When a water-swollen polyelectrolyte gel is interposed between a pair of electrodes and DC current is applied, the gel undergoes electrically-induced chemomechanical contraction and concomitant water exudation in the air. Tn order to clarify the mechanism, a one-dimensional electrokinetic model of the contractile phenomenon of polymer gels under an electric field was postulated based on Poisson-Boltzmann and Navier-Stokes equations. This model well characterized the nature of the contraction profiles and theoretically predicted that the rate of contraction linearly depends on the electric field, and the contraction efficiency inversely depends on the cross-linking density. The model also showed a good agreement with experimental data and qualitatively demonstrated that the electrically-induced contraction of the gel is dominated by electrokinetic processes of hydrated ions and water in the polymer gels.