Abstract：The paper studied a method that inverted resistivity distribution in crosshole section song crosshole low-frequency electromagnetic surveying data. First,a vertical magnetic dipole on bole axis is selected as a field source and assuming calculated medium is axis symmetry in respect of dipole axis,so,the model can be treated as a 2-D problem. Total field is divided into two parts:background field and scattering field in forward modeling concerning with each iteration in the article，the background field is calculated by FFM numerical approximation;using normalized least square fitting inversion technique in inverted calculation,resistivity section of subsruface medium can be reappeared from crosshole electromagnetic surveying data,us-ing reciprocity principle for calculating Green function and getting partial derivative of electromagnetic ;0esponse with respect to resistivity,the computing accuracy and efficiency can be improved. Results of model reappearance show that the electromagnetic imaging method is suitable both for high resistivity contrast model and for low resistivity contrast model. Vertical resolution of image improves with increasing frequency and improvement of lateral resolution relates to the factors such as frequency,interval between source and receriver and distance from anomaly body to borehole. numeric modeling results demonstrate that best working frequency must be selected according to adjacent bed resistivity.
