Based on the Nordholm's concept of Coulomb repulsive hole for plasma, a model of effective Coulomb potential is proposed to describe the charged fluids. Employing the classical density functional theory, the equilibrium structures of charged fluids confined in nano-cavities are calculated. Through the comparison with the numerical results, the effect of Coulomb correlation on the structure and excess adsorption is studied. In addition, the influence of Coulomb correlation on the structure is also calculated and studied under the condition of larger confinement. It is shown that the effective pair potential proposed here can be successfully used to predict the effects of Coulomb correlation on the structure and other physical chemical properties. Results obtained can provide some useful clues to the understanding of the correlation in other complex model potential system.