Four-electrode method is one of the well-known methods in measuring ground resistivity. But, most faults currents and lightning currents have high frequencies components. It is proposed to develop this method to study ground frequency characteristics. A step like current was injected into ground to measure the ground impedance. The ground impedance is assumed to be frequency dependent parallel resistance/capacitance. Two equations were proved to estimate ground resistivity and permittivity from four-electrode method. An analytical model was proposed to model studied cases. The four electrodes are divided to equal spheres and complex image method had been used to satisfy the boundary conditions and penetration depth effects. The calculated results show good agreement with the measured results.