Abstract: A model of dipole orientation distribution for solvate layer at electrode/solution interface was suggested, and based on this model a generalized monolayer adsorption isotherm was derived by using the method of statistical mechanics and assuming the equilibrium condition of thermodynamics. The solvent of the electrolyte studied may be single component or multic-components (mixture). The dependence of inner-layer differential capacity upon snrface charge density at mercury electrode in formamide, methanol and ethylene carbonate solutions was estimated by curve-fitting respectively. The present model is more suitable for aqueous and mixed-solvent systems will be expected.