This paper deals with the properties and applied ranges of different numerical calculation methods in 3D forward simulation for mine direct current method, puts forward the application of logarithmic even space and arithmetical even space to dissecting the discussed model, and explains the geological conditions met by electrode interchange. Considering the "non-biggest" diagonal elements characteristics of the coefficient matrix, the paper adopts the "big-data" processing method to fit the calculation method of the available linear equations. Through discussing some concrete problems, the authors expound the interrelationship between calculation precision and calculation time of the geological model, thus providing theoretical basis for selecting model parameters.