Abstract: The common track measurement is often used in scalar measurement of CSAMT. That is using electrical signals of the measurement of synchronous observation profile and a track signal of the vertical measurement to calculate the Cagniard apparent resistivity. For the different measurement position of magnetic field, there is impact on the measurement results. This paper deals with the influence of the different position of magnetic field on apparent resistivity measurement under homogeneous half space, and the influence of the different position of the equatorial magnetic field on apparent resistivity when the 3-D local anomalous body is excited. The apparent resistivity error caused by measuring position deviation of magnetic field is difficult to be corrected. Therefore, single magnetic single power measurement should be used in practical work, and single magnetic three powers should be used when the transceiver distance is large or the shallow electrical structure is uniform. It has important guiding significance for the research on scalar measurement of CSAMT and practical exploration work.