This paper deals preliminarily with the problem of direct-current electrical sounding for three inclined layers. Using the mathematical model for three inclined layers, the author conducted lots of forward calculations of electrical sounding with reference to various parameters such as dips of the first and thesecond inclined layer, variation in resistivity for every inclined layer, and the cases when the line parallel, perpendicular and oblique to the strike of the inclined layer respectively. The results of the calculations indicate that the values obtained are quite different from the results of electrical sounding for three horizontal layers, e. g., the difference in asymptotic values of tails of the curves;the distortion of electrical sounding curves when electrodes are arranged perpendicular to the strike of the inclined layer;the impossibility for electrical sounding curves to reflect correctly underground geoelectric cross section with certain geoelectric parameters. Consequently,when theoretical calculations for three horizontal layers are used to interpret three inclined layers, due attention-should be paid to the interpretation errors.