This paper proposes a useful technique for generating all earth resistivity map. Earth resistance is one of essential factors In a broad range of power system analysis and design. Information of earth resistivity is helpful for practical power system engineers in order to establish power system grounding. In this paper, a LANSAT7 image of a tested area of 50 km(2) was used by ENVI program in associative with a set of resistivity data obtained from field measurement. By using the maximum likelihood for Supervised classification of a mixed band 7, 5 and 3, highest value of 85.71% confidence was obtained.