Abstract:The paper discussed the issue how to select the data rotation direction in 1-D and 2-D MT inversion by correlating and analyzing the inverted results of 2-D and relevant 3-D theoretical model responses,which discovered that it is appropriate to use the main axial data for inversion in true 2-D situation.In this case,if using the data rotated into line direction,it demands that the angle between line and structural dip can't be too large (can't be greater than 30° in the model presented in the paper,for example).In 3-D situation,the more optimum inverted results than that using the data rotated into line direction may not be obtained if 2-D inversion is to use the data rotated into optimum axis direction.Since the practical-surveyed data are generally viewed as 3-D response,so,the paper considered that in practical data processing,in condition of clear structural trend and line nearly vertical to structure,the 2-D inversion is carried out after directly rotating the data into line direction,avoiding the difficulty selecting polarization mode on optimum axis direction.