Abstract: A model of EEG source is set up as a time-harmonic equivalent current dipole model which deals with the problem concerning the capacitance effect. The expressions of potential distribution in homogeneous infinite dielectric and homogeneous dielectric sphere on the electroquasistatic condition is given and the potential distribution in a three-layer inhomogeneous isotropic concentric sphere produced by the model is computed. The effects about potential distribution by time-harmonic character and permittivity are discussed. The theoretical calculation shows that potential distribution is effected by time-harmonic character and permittivity.