Abstract: In order to identify the overburden thickness,the distribution of weathering crust zone,weathering cap-sule and fractured zone,and to subdivide unfavorable geological condition within a tunnel,the authors use CSAMT method in the survey work. Because the surveyed area closes to the power station and its large substation,electro-magnetic interference is very strong,and the data obtained is not good. In order to improve the inversion precision,the genetic algorithms(GA ) inversion method is introduced. The inversion result by GA is much better than the re-cult reached by linear inversion method.