Abstract:The resistivity 3-D inversion method that involves conjugate gradient iterative operation is a new efficient method. It only estimates Gx (product of Jacobian ma- trix G and any vector x)and GT y(product of GT and any vector y), and avoids direct derivation of G and GTG, thus reducing operation greatly. Then, authors dedace Rodialgorithm for estimating G, and give the expansions of Gx and GT y in E-SCAN 3-D data inversion. It is found from minute analysis that Gx and GT y can be deduced simultaneously in once forward operation to achieve single forward operation for each inverse iteration, thus speeding up operation greatly. In addition, sensitivity matrix is analysed;and resolution outside E-SCAN area is discussed, which is significant to inverse interpretation of real data.