The paper presents the application of the Cole-Cole model for determining the runs of the return voltage of the paper-oil insulation sample through a computer simulation. Different insulation conditions were simulated through an adequate selection of parameters alpha and tau of the Cole-Cole model. For calculation purposes, a series-parallel substitute scheme, obtained through approximation of a discrete characteristic operator impedance Za of the model applied, was used. The diagnostics of the simulated insulation condition was based on the analysis of a few selected parameters of the return voltage, obtained from time characteristics.